I wasn't going to reply since those I've met aren't huge but as I don't recognize most of these people I might as well
I've met Kevin Smith (director of Clerks, Chasing Amy, Dogma, Red State, etc) and Marilyn Ghigliotti (Veronica in Clerks) on separate occasions. Brian O'Halloran (Dante in Clerks) and Marilyn wishes me a happy birthday every year because we're facebook friends like that. I also met Adrian Beard, who voices Token on South Park and pretty much all the other black characters as well as one of the lead storyboard artists. I met all the other lead artists too, got some awesome drawings from them. Matt Groening gave me a drawing he did of Charlie Brown last year, that was pretty much the highlight of my year.
Oh, and I met the entire original broadway cast of Book of Mormon, I brought ceramic frogs for them to sign long before they sold frogs in their broadway store and they all couldn't get over us bringing our own frogs so they always came to chat with us. The leads are doing pretty famously now, Josh Gad is on 1600 Penn now and Andrew Rannells is Bryan Collins on The New Normal.
But perhaps greatest of all was meeting the sheep farmer who owns the sheep farm Hobbiton is built on. I got my picture with him and everything.
That dude that plays Spock in the Star Trek films--
No, not Leonard Nimoy. That other, younger guy. Whatshisface.
I was at a cafe in NYC with a friend and he suddenly sits in the table next to us. My friend went into silent hysterics (while trying to remain cool). I had no idea who he was. If I saw him again I'd have no clue he was anybody famous. The only trekkie I know IRL is a TNG fan.