Surely I'm not the only person here who has met Dave Sutherland!
[Edit: I also once gamed regular-ish with Kelley Foote who designed the OA adventure "Swords of the Daimyo" for TSR. We played mostly Deadlands and Deadlands HoE, oddly.]
I've met John Tweet twice, once while he was working on Ars Magica and another time at GenCon when he was undoubtedly secretly working on third edition. I first met Rob Heinsoo at a Glorantha-Con when he was the new hire in charge of marketing at Chaosium, I think.
I've met and spoken to Larry Elmore every year GenCon has been in Indianapolis. He really is one of the nicest guys you could hope to speak to. My wife had Larry autograph a print she bought for my birthday, and every year he remembers us and what print she bought. He even offered to drawn my 5 yo daughter as a mermaid which of course thrilled by daughter to no end. Sadly, the last time I spoke to him, he hadn't gotten to it yet (and I certainly wouldn't hold it against him if he never did).
I've met Ed Greenwood a couple of times at a local convention. I had dinner with him (the perks of running the con!) and he's signed all my D&D books that he had anything to do with.
He's a really nice guy, and definitely shows where "Elminister" gets his personality traits from!
I voted 6 people (Gygax, Arneson, Zeb Cook, Greenwood, Grubb, Skip). I've undoubtedly "seen" at least a couple more in all the years I was going to GenCon (1988-97) but if I wasn't able to put a name to the face at the time I'm not counting 'em.
I met Jeff Easley when he did the cover artwork for a small game company I worked for right out of college. I had the task of going to his house to take a photo of the completed work, since the print was going off to the printer and it would be weeks before we would see the final product.
I remember Mr. Easley graciously greeting me and when I walked into his house I felt almost overcome by vertigo as I walked into his (I believe) living room that was completely wall to wall pieces of his iconic d&d artwork. Seeing all of that art that I had grown up with on books and magazines in this impromptu (and very unexpected) manner was a very cool moment.
I also spent time in the National Guard with Gary Gygax's son, and in turn I had a few email conversations with Mr. Gygax and it turned out that he had known my grandfather who had been a police authority in the area he lives in. It was interesting to hear stories of my grandfather I had never met from such a source!
I've met James Jacobs and he signed a book for me.
Does it have to be D&D? I've met a few of the crew from Palladium books, including Kevin Siembieda. I actually was in a three way convo with Kevin S. and Joly Blackburn at Gencon in 2006.
I almost accidentally ran into Margaret Weis at GenCon.
I don't know if he's "famous" but I've got mutual friends with Nick Logue and even played Shadowrun with him DMing.
I've not met any on the list but, however, have been lucky to have met Erik Mona and Sean K. Reynolds at Stellarcon. Both great guys! I was in a game Erik ran at MACE and had breakfast with Sean in which I told him how much I wasn't thrilled about the 3.5 Ranger after having mine die 3x after I'd converted him from 3.0 to 3.5.
Edit: Also met Margaret Weis and Tracy Hickman at Dragoncon on several occasions. And also former game writer Aaron Allston.
The problem with this poll is that relatively few of those mentioned would be easily recognized, even by fans. It's like asking how many radio celebrities you've seen/met.