Would love to see Pete Holmes and TJ Miller on together, just to see if Scott could get a word in edgeways.
Highly improbable, but would love to hear some English comedians on the show - Ross Noble, Stewart Lee, the Boosh, Dylan Moran, Daniel Kitson,Jimmy Carr, Kevin Eldon, Mark Gatiss, Chris Morris, Steve Coogan, the list goes on...
Simon Pegg and/or Edgar Wright would be great too.
As someone else suggested, a Community cast show would be awesome. Gillian was great on her recent appearance.
I'm always happy with Kroll, Tompkins and Wittels though.
