Guests on The Big Bang Theory: Where Is That Person From?

Premiering in the fall of 2007, The Big Bang Theory features a ton of familiar faces. Principals Johnny Galecki and Melissa Gilbert were the on-again, off-again high school romance on the sitcom Roseanne. You may also recognize Jim Parsons from his bizarre 2003 Quiznos commercial or Mayim Bialik of Blossom fame.What about the cameos and guest stars? If you are frequently left asking "Who is