I would do awful, unspeakable things to get Lem from
http://bunny-comic.com/.
Since he's in Britain, I'd second just about everyone Tobias and BabakganoosH mentioned. Especially Mr. Clevinger. While I'd do awful, unspeakable things to have Lem come to Intervention Con, what I'd do to ensure Mr. Clevinger's attendance would only be a few steps lower than that.
Anthony Clark of
http://www.Nedroid.com would be a great get, Aaron Diaz of
http://www.DresdenCodak.com would be great, and, if he's not TOO busy, Chris Eliopoulos of
http://www.MiseryLovesSherman.com would be sweet - not only because his comic kicks ass, but also because he letters pretty much everything Marvel does. And he's a riot.
Oh - crap, almost forgot about one of my favorites that hasn't been mentioned,
http://www.DrMcNinja.com with (edit:) CHRIS Hastings. Shit, he could bring Commissioner James Gordon! I mean, the little fluffball almost won the All American Pet Brands Cutest Dog competition - that would be a HUGE win! (And his comic is pretty spectacular, too. He's also based in NYC. So the minimal travel distance is a plus.)