David Copperfield - My wife and I were at one of his shows and I was randomly selected (by catching a beach ball) to come up on stage for the show's finale. Along with dozen other people, I sat down in a chair on stage. A curtain was pulled to hide us from the audience, and when the curtain was opened the seats were empty and we are all in the back of the theater waving. Then they took us all backstage where we met Copperfield, got autographed pictures, and watched a video of the trick from the audience's perspective. He also asked us not to reveal the secret of the trick, although to tell you the truth, even though I was part of it, I have no idea how much of the trick was done. It was a blast!
This video is not the show I was in, but this the trick I was a part of:
I also met a few minor celebrities when I worked as crew for concerts and events at the local civic center way back in high school (mid 80s). It was mostly country music concerts, but we had one wrestling match. My job was to stand at the door and direct the wrestlers to the right dressing room: "Good Guys" on one side, "Bad Guys" on the other. The only really big name was Mick Foley (aka Mankind although he was called Cactus Jack then) and he was probably the least fun of all of them. He wasn't rude, but it was obvious that he took his job much more seriouslly than most of the others. Most of them were laughing and joking around all night, but Foley was all business.