I met Muhammed Ali in the Cleveland airport. He could barely talk or walk without help yet was gracious enough to sign some autographs.
I got a huge hug from Allyssa Milano (nom, nom) when I was at a bar where her bf was playing.
Played hockey a few times with Brett Gretzky, we called him "The Good One" I know he's not famous but since his brother is, I figure that's a celebrity meet, once removed.
I met Magic Johnson when he played for MSU.
I've met tons of magicians, the most famous that non-magicians would know are probably Penn, Teller, David Copperfield, and Lance Burton.