Ernie Hudson at a comic con before. Nice, relaxed guy. I also had Edward Furlong (John Connor from Terminator 2) begrudgingly shake my hand when I caught him outside smoking at a different comic con.
I almost met Marilyn Manson for a book singing, but the event closed before I could make it up to him in line. However, my dad was present, knew I was going to get screwed out of meeting him, and got the man to sign a book for me anyway (and personalize it, which was against the rules)!
On a less famous scale, I met both Mike and Jay from Red Letter Media (the guys behind the Plinkett Star Wars: Phantom Menace reviews). A friend of mine who was with me had their interest a bit because he told the RLM guys that he used to work with Rich Evans (the guy who plays the "other Plinkett" in the Half in the Bag series) at a grocery store.
Also, another friend of mine met the Nostalgia Critic while working at a Starbucks. The Critic lives just north of where I live, so I knew it was a matter of time before me or someone else I knew would run into that guy!
I think that about covers it for me!