Peter Wintersteller/Berliner

In spite of Kristen Bell’s busy acting career, the Couples Retreat star still took the time to make saving the world look stylish. Last week, Bell joined Pete Wentz and Rachel Bilson to co-host the Guess/Vanity Fair party in Los Angeles to launch special edition organic Guess T-shirts that benefit the nonprofit organization Invisible Children. Pairing one of the T-shirts with a sexy Vena Cava dress and Christian Louboutin pumps, Bell talked to PEOPLE about her involvement with the organization, which promotes youth education and economic development in war-torn regions of Central East Africa. “It’s just standing up for humanity, which I think is really important for us to do for each other,” she said. Bilson agreed, saying, “It’s also important to spread the word about these T-shirts. You can buy them, and all the proceeds go to Invisible Children.” The party stayed lively with Wentz behind the DJ booth and attendance by celebrity friends such as Annalynne McCord and Eliza Dushku with boyfriend Rick Fox. Buy your own Guess Invisible Children T-shirt for $26 on Guess.com, with 100% of the proceeds going to the organization. –Susan Yara

Richie Buxo/Splash News Online

From dying her hair black to her new rock ‘n’ roll style, Kristen Stewart is really getting into character. While filming a Joan Jett biopic, Kristen has adopted a uniform of vintage rock tees and skinny jeans, and has even gone so far as to hang out with the rock legend she is portraying. (We can hardly tell them apart!) While this new punk look is genres away from Twilight’s Bella Swan, we think Kristen totally pulls it off. Just yesterday, she turned up to Comic-Con in another Chaser T-shirt featuring early-’80s hardcore punk band Minor Threat. And what’s better, it’s totally affordable! Get Kristen’s Chaser “Minor Threat” T-shirt, $22, at chasermerch.com..

Courtesy of H&M

For its second season of Fashion Against AIDS, H&M has teamed up with stars like Katy Perry, Dita Von Teese, Estelle, Cyndi Lauper, Yoko Ono, N.E.R.D and more. Each star has collaborated with H&M on designs for T-shirts, T-shirt dresses, vests and bodysuits to spread the word about safe sex through bold slogans in vibrant colors. Katy Perry’s safe sex message, “It’s What’s On The Outside That Counts,” is printed in bright script on a body suit and T-shirt. Dita Von Teese offers an alluring image of her iconic red lips and arched brow on a cute cap-sleeved T-shirt while Cyndi Lauper takes an 80’s approach with her iconic slogan, “Girls Just Want to Have Safe Sex,” scrawled in what looks like hot pink lipstick on a tank top. The collection will hit H&M stores on May 28, with 25% of the sales of each item will be donated to youth HIV/AIDS awareness projects.

Credit: Bauer-Griffin; GSI Media; Flynet

Not only did Rachel Bilson take a front-row seat at pal Brian Reyes’s show during N.Y.C. Fashion Week last Thursday, but she’s his best model on the streets of Los Angeles this week! The newly-engaged actress wore not one but three of Brian’s tops this week. First, she wore out his gray T-shirt with black layers, switching to his white T-shirt with Helmut Lang jeans the next day. She just keep going pairing her Brian Reyes marble-print top with a black vest and wide-leg pants. We’re loving her accessories too — check out her red Miu Miu purse and her green Chloe chain strap. No wonder Rachel is one of our favorites for her off-duty style savvy. Buy a Brian Reyes T-shirt for yourself at shopbop.com, $240.

Pacific Coast News

No matter what’s happening in her life, Madonna is still in love with British brand Bodas’s organic supima cotton T-shirts. The singer wears them “to work out, to run errands, to go out — she loves them for everyday,” a source tells PEOPLE. (She also likes them for primetime — she wore a black short-sleeve T in her 4 Minutes video with Justin Timberlake.) A Bodas spokeswoman tells PEOPLE that the singer most recently purchased a handful this summer. “She wears them out, and then her assistant comes in and buys five more,” she says. And unlike, say, Madonna’s one-of-a-kind designer tour outfits, you can actually purchase these looks. They’re $90 for a tank top or short sleeve, and $98 for long-sleeve styles, available at www.bodas.co.uk or at Barneys New York. – Courtney Rubin

John Sciulli/Berline

Show your love for one of TVs most fashionable zip codes by wearing a 90210 T-shirt. CBS Consumer Products and 90210 have partnered up to release an array of vintage-style tees available at Kitson Studio in West Hollywood. The collection was unveiled this week during an intimate soiree at Kitson with a handful of cast members, including Dustin Milligan (Ethan), Jessica Stroup (Silver)– in LNA– and Ryan Eggold (Ryan). As guests sipped cocktails and shopped for T-shirts, the band Karmina performed “The Kiss,” which was heard in an episode of the CW’s 90210. The T-shirt designs include a classic cast shot from the original 90210 and another one that says, “Meet Me at the Peach Pit.” If a version from the newer West Beverly is more your style, choose sides by wearing either a “Team Naomi” or “Team Silver” T-shirt. The $28 shirts are available at the Kitson store on famed Robertson Boulevard or at www.shopkitson.com.

Starbux / WENN

In light of the terrible plane crash that left Travis Barker and DJ AM badly burnt and four others dead, Barker’s Famous Stars and Straps clothing line is producing exclusive T-shirts in memory of the former Blink 182 drummer’s personal assistant Chris Baker and security guard Charles Still. The shirts were designed by pro skater and Famous team manager Felix Arguelles and Famous art director and artist Maxx “maxx242″ Gramajo. All the proceeds from sales of the shirts will benefit the memorial funds set up for Chris Baker and Charles “Che” Still. A source tells PEOPLE, “Everyone that is a part of the Famous family are really close, so Chris and Che were brothers to everyone. The shirts were made to honor them and support their families.” The memorial T-shirts will be available exclusively at Famoussas.com and at The Fast Life store in L.A.

INF

Sarah Jessica Parker made a subtle political — and fashion — statement while running around New York City yesterday in her Obama-inspired “Dare to Dream” tank. Her coveted tank is actually Zac Posen-designed and part of Barack Obama’s “Runway to Change” initiative. Posen isn’t the only designer to lend his talents to the campaign. Joining him in creating exclusive “Change” T-shirts, tanks and accessories are other top names like Nanette Lepore, Tory Burch, Russell Simmons, Vera Wang, Tracy Reese, Alexander Wang, Narciso Rodriguez, Beyonce and Tina Knowles for The House of Dereon and more. Your purchase of one of the Ts will count as a campaign contribution. Check out all the designs, at barackobama.com.

Julian Broad; courtesy Saks Fifth Avenue

Following in the foot steps of past stars like Hilary Swank, Charlize Theron, Renee Zellweger and Glenn Close, Gwyneth Paltrow has been named the Entertainment Industry Foundation’s (EIF) ambassador for Saks Fifth Avenue’s 2008 KEY TO THE CURE campaign, a women’s cancer initiative founded in partnership with EIF’s Women’s Cancer Research Fund. The limited edition T-Shirt modeled by Gwyneth was created by legendary designer Karl Lagerfeld and features a cross bow and arrow on the front and a sketch of Karl himself on the back. Gwyneth will appear in all KEY TO THE CURE ads and a public service announcement wearing the T-shirt. Karl’s limited edition work will hit Saks Fifth Avenue stores and their website on October 1 and retail for $40 with over $35 to exclusively benefit KEY TO THE CURE. In the ten years since Key to the Cure’s inception, Saks and its partners have raised more than $28 million. Tell us: What do you think of the new KEY TO THE CURE T-shirt? Would you buy one?

INF, BuzzFoto

We first spotted Nicky Hilton in her whimsical Vogue t-shirt earlier in the week, and then we spotted Ashley Tisdale in her equally adorable illustrated T-shirt yesterday on a shopping spree at Kitson. Turns out the hot tees come from Trash & Luxury, a glam new line by L.A. designer Hushi Mortezaie. It seems he got his quirky style from his mentor Patricia Field– the famed Sex & the City stylist responsible for SJP and cast’s outlandishly fashionable costumes. When it comes to his own line, Hushi Mortezaie designs T-shirts that meld a glamorous spirit with a hint of comfort– and what is more glamorous than Vogue? For the first Trash & Luxury collection, Hushi takes his inspiration from ’80s-era New York, the real-life dream world of Los Angeles, Hollywood by night — and a magazine that’s earned its own song. Love the Vogue tees? Get Ashley’s Trash & Luxury tops, $48, at shopkitson.com and Nicky’s, $48 , also at shopkitson.com

Roger Walsh /Landov

Former Primp designer Alexx Jae launched a line of organic t-shirts for the Environmental Media Association on February 13 at one of LA’s premiere fashionista havens, Milk, whose clients include Zooey Deschanel, Rachel Bilson, Mandy Moore, and the Simpson sisters. “People think the environment is so not cute or hippie-ish, and I wanted to show that it could be really hip and cute,” says the L.A.-reared designer, who no doubt was inspired by her mom, the head of EMA. The super-soft tees and cardigans feature pro-environment messages written in light ink, like “Where’s your hybrid?” and “Compact fluorescents are sexy.” “I would never wear anything with a saying so loud so I wanted to make it very subtle,” says the environmentalist, who also uses bamboo in her sophisticated high-end collection, due out in the fall. Emily VanCamp, for one, was sold on the message: “I think it’s fabulous! I bought a cardigan. I’m all for a healthy environment, healthy clothes.” Other celeb fans: Anna Faris, who hosted the party, Amy Smart, Heather Graham, and Alexx Jae’s childhood BFF, Nicole Richie. “Nicole wears my stuff. She has to!” says the designer, who will donate 100% of the proceeds to EMA. Click here to buy the t-shirts, $75, at shopatmilk.com.

Most Wanted/Flynet

The heiress wants to save the world — and soon! Paris Hilton was recently spotted leaving the Kate Somerville spa in L.A. sporting the limited edition DOE Power Puff Girl Tee. In honor of the 10th anniversay of the girl power cartoon, The Cartoon Network has teamed with t-shirt designer DOE to create this adorable tee promoting a “Green” world. Unfortunately, this Power Puff Girl tee was created exclusively for celebrities and won’t be available in stores or online anywhere. Such famous faces who have been given the tee include Miley Cyrus, Hilary Duff, Hayden Panettiere, Megan Fox, Drew Barrymore and Ashley Tisdale. If you love the Power Puff Girls, you can also get a DOE vintage wash tee, $25, at babygirlboutique.com.

courtesy shopwhateverittakes.com

Sometimes it feels so much better to give than to receive — especially with Valentine’s Day fast approaching. Celebs, including George Clooney, Lucy Liu, Gwen Stefani and Nicole Kidman, seem to agree. They’ve all designed custom art for tees as part of Wildcat Apparel’s new “Whatever It Takes” campaign. Each tee sold ($48) helps benefit global initiatives such as poverty and environmental conservation. Click here to buy your tees online, or find them now at boutiques nationwide, including celeb favorite FrontRunners in L.A. Plus check out more great Valentine’s gifts in the current issue of PEOPLE, on newsstands now.

Eric Liebowitz/ The CW

We’ve already seen Halle Berry show her support for Barack Obama in style, and now the cast of Gossip Girl is joining the political fray by urging voters to rock the vote! Blake Lively and her stylish co-stars are rocking this T-shirt by Society and now you can too! Click here to buy a Rock the Vote t-shirt for yourself at shopkitson.com,$38, and click here to register to vote at rockthevote.com.

Chris Graythen/Getty

We are so blown away by Brad Pitt’s generous donation of his time and $5 million of his own money, as well as the donation of design work from thirteen of the country’s best architects to rebuilding the Ninth Ward of New Orleans. While most of us can’t afford to pony up $150,000 to fund an entire house or $5000 for a generator, we can buy t-shirts like Brad’s and help support the Make It Right project. Click here to buy a t-shirt, $20, or driving cap, $30, to benefit the Make It Right project and help rebuild New Orleans. Check out makeitrightnola.org for more information on the project.

RAMEY

No doubt about it, Zac Efron loves his t-shirts. Over the past few months we’ve spotted the High School Musical 2 star in just about every style imaginable. While we love it when he wears a classic solid-color look like fitted white, basic blue or black, we’re even more enamored of motifs like graphic waves and his message t-shirt look. When we spotted Zac again in his latest favorite, we just had to hunt it down. You can snap up one of the retro-styled Nike shirts emblazoned with the motto “Just Do It” in faded blue online at urbanoutfitters.com, $32. Tell us: What do you think of Zac’s T-shirts? Do you love the look, or do you prefer him a little more suited-up?

Click here to get your own Just Do It t-shirt, $32.

Alex Turner/Splash News online

Following the lead of boyfriend Zac Efron, Vanessa Hudgens is getting her message out there — on her trendy t-shirt! While out for lunch with her mom and younger sister, the High School Musical 2 star pushed for “Peace Now” with her Lux t-shirt. You can get your own t-shirt for $28 at urbanoutfitters.com. Tell us: Would you wear Vanessa’s t-shirt?

Jack Ludlam/Splash News online; Cousart-Ramirez/ JFX

This summer we’ve spotted loads of stars like Jessica Alba, Fergie, Nicole Richie, and more sporting comfy, brightly-colored t-shirts. After a little digging, we found out these tees are from a cool new company called LnA that launched this past spring. The collection, which ranges from $55 to $70, includes everything from sexy deep V-necks to muscle tanks in bright colors like violet, canary yellow, and cherry red. The lure of the tops is their super soft cotton and flattering fit. We’re definitely looking forward to wearing the company’s long-sleeved tees this fall. Get Jessica Alba’s basic crew neck, $60 at revolveclothing.com or Fergie’s V-neck, $65 at intermixonline.com.

Anthony Dixon /WENN

Not exactly afraid to express his opinions, Ashton Kutcher sported an “I Have Issues” t-shirt while filming What Happens in Vegas…. The simple, but definitely eye-catching, t-shirt is a part of the “Awearness” campaign by Kenneth Cole. All the graphic T-shirts in the line make references to societal problems, whether it’s global warming or identity theft. The best part is that for each t-shirt sold, $10 is donated to the Awearness Fund, which fights AIDS and helps the homeless. All styles are available for both men and women and retail for $35. Find your perfect message today at kennethcole.com.

Matt Symons-Andy Johnstone/Pacific Coast News

Taking a break from promoting the mega-hit High School Musical 2, Zac Efron hit the gym for a quick workout. But not missing an opportunity to make a very literal style statement, Zac pounded the pavement in a t-shirt proclaiming “Reverse Psychology Doesn’t Work.” Could it be words of wisdom, teenage angst or just a comfy tee to work out in? Whatever the reason, you can purchase Zac’s Vintage Vantage brand t-shirt at balcony.co.uk for 16GBP or approximately $32.