I have a few favorites I'd like to see on the show. However, the likely hood of them actually being on would be slim, probably.
1. Matt Damon- he knows how to do all the spy stuff from Bourne Identity and he's cute
2. Steven Spielberg- he's a big fan. that;s how JG ended up in Catch Me if You Can. he could play some evil scientist or something
3. Ben Affleck- he can do action too, and he's cute.
4. Natalie Portman- i just think it would be interesting to see her on the show.
5. Keri Russel- hey, J.J. has brought other past Felicity stars onto Alias, why not Felicity herself. Afterall, JJ got the idea for Alias by wondering what would happen if Felicity was a spy.
I'm sure I'll come up with more, but if you ask me, I think that is a pretty good list.