20x10: People who were in other things before they were in the things they're in now, what they used to be in, and what they're in now

Jane Krakowski as "Elaine" on Ally Mcbeal, now "Jenna" on 30 Rock

Lisa Edelstein as "Cindy McCaulliff" on Ally Mcbeal, now "Lisa Cuddy" on House

Johnny Galecki as "David" on Roseanne, now "Leonard" on Big Bang Theory

Joshua Jackson as "Pacey" on Dawson's Creek, now "Peter Bishop" on Fringe

Greg Grunberg as "Sean" on Felicity, "Eric Weiss" on Alias, a pilot on Lost, now "Matt Parkman" on Heroes

Kristen Bell as "Veronica" on Veronica Mars, as Elle on "Heroes," now narrator of Gossip Girl

Katherine Heigl as "Isabel" on Roswell, now "Izzie Stevens" on Grey's Anatomy

Adam West as "Batman" on Batman, now "Mayor Adam West" on Family Guy

Callum Blue as "Mason" on Dead Like Me, as "Bob" on Related, as "Anthony Knivert" on The Tudors, now "Zod" on Smallville

Adam Baldwin as "Jayne Cobb" on Firefly, as "Chad" on Daybreak, now "Agent Casey" on Chuck