Nicest famous person I've ever met was Derren Brown - did a meet and greet thing with him, he was adorable. Smashing chap! (Although I hear he likes to now).
Kevin Spacey impressed me for not freaking out at all the attention he was bring given. He posed for pictures and signed autographs, and didn't seem to bother him.
Think the only other people I've met have been football related. Met alot of past-players, current players and managers down the years - GH, Thommo, Sammy Lee, Rafa a few times, Nigel Spackman (loved this), Danny Murphy was class, Carra, Paul Walsh Rush, Aldridge (always a gent), Alan Kennedy, Phil Neal, Clem, Lawrenson, Hansen and a few others. I remember meeting the Spanish lads - Alonso, Garcia and Nunez shortly after they had signed and not knowing who they really were or which players were whom. I find that funny now.
Met a few tv-football personalities too - Linekar, Matt Smith, Alan Smith (nice guy), Alan McInally. Met Henry Winter too - he was nice and chatted for a while.
To be honest, the only famous person I ever met who I thought was a complete twat was Phil Neal. Didn't want to talk to anyone, came across as moody and arrogant.