I played go, chess and many other games. Poker is widely avaible online, could be played for free or money and is quite "dirty". Never seen Jessie James playing chess :P.

Well, the money aspect didn't even figure in the original article as a positive, and go, chess & various other card games contain math, too, and often have quite vibrant online communities.

And, erm "dirtyness" as a deciding factor? Then I'd suggest three card monte.

LOL. :)