Kevin Rose gave away 4000+ Gmail invites and (we assume) all were taken in a few hours. If you want to try your luck at picking one that hasn't been used, I included the link:

http://kevinrose.typepad.com/allthegmail.html

oh and i'm still updating my old post with new invites as I get them. here's the permanent link:

"Want a Gmail Account? I got a few spare"