Let's see...
Lou Gossett Jr, when he was taping one of those short video interviews that used to play on the monitors around Disney-MGM Studios back when it first opened.
Kurt Warner and Mary Lou Retton at ESPN the Weekend, I think it was in 2005.
The lovely and talented Eartha Kitt doing the narration at the Candlelight Processional. She was fantastic. She sounded like a minister giving a sermon and she was full of passion reading it. I'm not Christian, but even I was moved by her delivery.
I saw The Beach Boys and Davy Jones in concert during festivals at Epcot(Food & Wine for Beach Boys, Flower & Garden for Davy Jones)
I met Mike Shanahan(Denver Broncos Head Coach) when I was working at the Bell Desk at Boardwalk Resort and Inn. He came up and asked me where a good place to get a burger was. I hadn't realized it was him at first, just that he looked awful familiar, so I mentioned the ESPN Club being the closest. He told me he had to go there a little later anyway, so he'd make it his first stop. As he turned to go, someone that knew him personally was walking by and said to him "Jeez, they let anybody in here, don't they?" The two of them started laughing and his friend introduced a traveling companion to him.
I also got my picture with Amy Allen at Star Wars Weekend(She played Aayla Secura, the blue Twi'lek Jedi Master in Attack of the Clones and Revenge of the Sith)
I think that's about everyone I've seen so far. If I remember any others I'll post again.