9. Paul Scheer
Though many of you know Scheer best from The League, he's been all over the comedy landscape over the last few years: you can see him on adult swim's NTSF:SD:SUV, listen to his How Did This Get Made podcast, and even catch him from time to time on Yo Gabba Gabba.
Scheer's work with UCB began in 1998; as an improviser, he worked with familiar faces like Rob Riggle and Jack McBrayer. In 2005, he began collaborating with Rob Huebel, Aziz Ansari, and Jason Woliner, which became Human Giant, the group that spawned a show on MTV and launched their careers.