here's a few that come up in our drunken home games:

"Super Hold 'Em"-I think they're might be another name for it, but you're dealt 3 down cards, and then it's played like regular hold 'em, use any combination of the three in your hand and the 5 on the board

"Hold-'Em 64"-each player is dealt 4 down cards. the flop is 2 cards, the 'turns' are 2 cards, and the 'rivers' are 2 cards. make your best 5 card hand from any combination of the 4 in your hand and the 6 on the board. if you're sober enough, we occasionally play it with 2-7 lowball rules, and play it as a high/low split game