On Memorial Day weekend this year, DW and I ran into Dick Vitale at Tony's Restaurant. Although I already knew him through work, so it was more of the fact that I've never randomly ran into someone familiar at the parks without planning it.
Other than that, I ran into both of the Dukes of Hazard, who have apparently been sighted a lot in this thread, at MGM back in 1989.
Although I wish my cousin posted here, because he was a CM for over a decade back in the 80s/90s, and met tons of people. The only story I remember particularly sticking out was from when he was a bellhop at one of the resorts and John Travolta arrived to check in. He handled his luggage and took it to his room, and when Travolta tipped him, he gave him exactly $99. And as my cousin tells it, "Because of some weird religion he's into, I forgot what it's called, he couldn't actually give me $100." This was back in the early-90s before many people knew what Scientology was.