Post-All That Careers
Most significant works listed. Feel free to add more info as you know it.
Actually famous:
Kenan Thompson (Kenan & Kel, Saturday Night Live, Snakes on a Plane, Barbershop 2, Fat Albert)
Amanda Bynes (The Amanda Show, What I Like About You, Hairspray, Easy A, She's the Man, What a Girl Wants, Big Fat Liar, Robots, Sydney White)
Nick Cannon (The Nick Cannon Show, Wild N' Out, Drumline, America's Got Talent, Up All Night, HALO Awards)
Kel Mitchell (Kenan & Kel, Dance 360, Clifford the Big Red Dog, Attack of the Show, Mystery Men, Dance Fu)
Gabriel Iglesias (Last Comic Standing, numerous stand-up albums & specials)
Consistent work:
Lisa Foiles (editor-in-chief for Save Point, columnist for Kotaku, Top 5 videos for The Escapist, web miniseries The Street Fighter, assorted commercials, indie films)
Kyle Sullivan (The War at Home, Fillmore, Malcolm in the Middle)
Lori Beth Denberg (The Steve Harvey Show, Dodgeball)
Jack DeSena (Avatar: The Last Airbender)
Mark Saul (Grey's Anatomy)
Alisa Reyes (The Proud Family, Passions, indie films)
Jamie Spears (Zoey 101)
Not a whole lot:
Josh Server (Oh Yeah Cartoons, web series Laugh Out Loud TV)
Danny Tamberelli* (Eddie McDowd, rock band Jounce, live comedy group Manboobs)
Giovonnie Samuels (Freedom Writers, Bring It On 3)
Denzel Whitaker (The Great Debaters)
Leon Frierson (Bulworth, Snow Day, rap group The Circuit)
Angelique Bates (indie films, attempting music career as "Alizay")
Chelsea Brummet (guest appearances on many shows)
Kianna Underwood (touring production of Hairspray)
Bryan Hearne (raps as "Comodity" [sic])
Literally didn't try:
Ryan Coleman (finished high school, now re-attempting career)
Christina Kirkman (currently in college full-time)
Shane Lyons (retired from acting, became a chef)
Katrina Johnson (mostly retired from acting aside from a few indie films, became a flight attendant, then a bartender)
Christy Knowings (mostly retired from acting, guested on Sesame Street)
*Unlike the other cast members, Danny had a very extensive acting career before All That, so yeah. And Jounce is pretty successful for a Phish-style band.