Wow I was thinking about this exact topic yesterday.
My pathetic "wins":
A Magic: the Gathering tournament of about 50 people, 14 years ago.
I had the highest AHSME + AIME (math competitions
http://en.wikipedia.org/wiki/AHSME) in the state when I was in high school.
It's been all downhill since then. I've won several live poker tournaments with 50-100 players but figure those are largely irrelevant since there's so much luck involved.