1 of 20 Warner Bros/Everett Collection, Doug Hyun/TNT
After playing Chino bad boy Ryan Atwood, McKenzie did a full 180 when he took on the role of rookie police officer Ben Sherman on Southland. Unfortunately, the cop drama was canceled after its fifth season this spring.
2 of 20 Warner Bros/Everett Collection, Yahoo
Following his role as the adorable Seth Cohen, Brody made the switch to film, appearing in In the Land of Women, Jennifer's Body and Scream 4. He then joined Season 2 of the web series Burning Love, which will air on E! this fall.
3 of 20 Warner Bros TV/The Kobal Collection, Eddy Chen/The CW
Bilson, who played Summer Roberts, appeared in a few films including Jumper and New York, I Love You before returning to TV full-time in 2011. She now stars in Hart of Dixie, a CW series from O.C. creator Josh Schwartz.
4 of 20 Warner Bros/Everett Colletion, Barbara Nitke/The CW/Landov
After Marissa Cooper was killed off in the Season 3 finale, Barton struggled to maintain any career momentum. She appeared in a string of failed horror films before landing a role on The CW's The Beautiful Life. Unfortunately, the series was canceled after two episodes in 2009. Barton will next appear in the upcoming thriller Homefront alongside James Franco.
5 of 20 Warner Bros/Everett Collection, Ben Mark Holzberg/USA Network
Following his role as Sandy Cohen, Gallagher appeared in multi-episode arcs on Californication and Rescue Me. He now appears as CIA director Arthur Campbell on USA's Covert Affairs.
6 of 20 Warner Bros/Everett Collection, Doug Hyun/TNT
Kirsten Cohen always struggled with accepting who she was, but in Perception it can actually be hard to keep track! Rowan plays two roles on the drama, psychiatrist Caroline Newsome and Natalie Vincent, one of her patient's imaginary best friends and mentors.
7 of 20 Warner Bros/Everett Collection, Ben Mark Holzberg /The CW
Clarke's career never missed a beat after her role as Julie Cooper wrapped up. She went on to appear on Entourage and The Vampire Diaries, while continuing her decade-long recurring role as dominatrix Lady Heather on CSI. She now stars on The CW drama Nikita.
8 of 20 Warner Bros/Everett Collection, Richard DuCree/USA Network
After playing uptight over-achiever Taylor, Reeser appeared on Entourage, No Ordinary Family, Last Resort and Hawaii Five-0. She most recently appeared as Abby Bruce, a rival to John Stamos' sports agent character on Necessary Roughness.
9 of 20 Warner Bros TV/The Kobal Collection, Nicole Rivelli/CBS
Following his role as Jimmy Cooper, Donovan appeared on Damages, Argo and the now-canceled Deception. He will next be seen starring alongside Toni Collette and Dylan McDermott in the CBS drama Hostages.
10 of 20 Warner Bros/Everett Collection, Katherine Bomboy-Thornton/ABC
Carmack's character Luke had a hard time accepting his father's sexuality, but in his new role on Nashville he struggles to accept his own. On the ABC drama, Carmack plays Will, an aspiring country star whose afraid to come out.
11 of 20 Warner Bros./Everett Collection; TV Land/Everett Collection
After playing manipulative patriarch Caleb Nichol, Dale went on to play manipulative patriarch Bradford Meade on Ugly Betty and manipulative patriarch Charles Widmore on Lost. He also had roles on Entourage, The Killing, Once Upon a Time and NCIS beforel landing a spot in the Hot in Cleveland cast.
12 of 20 Warner Bros./Everett Collection; Jack Rowand/The CW
Holland replaced Shailene Woodley as Marissa's younger sister Caitlin in Season 3. Schwartz then cast her as another bad girl, Agnes Andrews, on Gossip Girl. Now, she's starring on The CW's Arrow as Oliver's sister Thea Queen.
13 of 20 Warner Bros./Everett Collection; Summit Entertainment
Gigandet, who played bad boy Volchok, continued his villainy as James in Twilight. He went on to star in Easy A and Burlesque, alongside Christina Aguilera.
14 of 20 Warner Bros.; Sonja Flemming/CBS
Following her role as Theresa, Rawat starred on Numb3rs as Amita Ramanujan, a mathematician and FBI consultant who marries Charlie (David Krumholtz). Since the series ended in 2010, she's also appeared on Castle, Burn Notice, Grey's Anatomy and Justified.
15 of 20 Warner Bros./Everett Collection; Sonja Flemming/CBS
Armstrong starred in films Just My Luck and It's a Boy Girl Thing following her stint as Seth's love interest Anna. She then played Juliet on the first season of Dirty Sexy Money before landing a guest-arc on The Mentalist as Summer Edgecombe.
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After playing bisexual bartender Alex, Wilde played Thirteen, a bisexual doctor on House. The actress then turned to the silver screen, starring in such films as TRON, In Time and Cowboys and Aliens.
17 of 20 Warner Bros./Everett Collection, Darren Michaels/TBS
Following his role as Summer's ex and Seth's friend Zach, Cassidy appeared on Smallville and Privileged. He had a small role in Argo, alongside O.C. co-star Tate Donovan, and now stars on Men at Work as Tyler.
18 of 20 Warner Bros./Everett Collection; Monty Brinton/CBS
Nouri appeared on Army Wives, Damages and All My Children following his role as Summer's dad Dr. Roberts. He also has made recurring appearances on NCIS since 2008 as Mossad Director Eli David. Nouri will next be seen as a Rabbi in the 2014 rom-com The List starring Karen Gillan and Jennifer Morrison.
19 of 20 Warner Bros./Everett Collection; Danny Feld/NBC/NBCU Photo Bank/Getty Images
After playing insufferable hippie Che, Pratt became everyone's best friend as Andy Dwyer on Parks and Recreation. During hiatus from the NBC comedy, Pratt also filmed roles in Moneyball and Zero Dark Thirty. He recently shed some weight and packed on muscle for his starring role in Guardians of the Galaxy.
20 of 20 Warner Bros./Everett Collection; Colleen Hayes/CBS
Righetti, who played Hailey Nichol, appeared on failed shows Reunion, K-Ville and North Shore before landing a starring role on The Mentalist as Grace Van Pelt. She also had a small role as a S.H.I.E.L.D. agent in Captain America: The First Avenger.