There have been a number of Pyramid articles on gambling in GURPS. If you subscribe it might be worth your while to check these out:
Gambling and Dice Games gives a few ideas for non-poker games. Worth looking at for some additional ideas.
Bet On It offers some mechanics for abstracting longer games and clearly had all night poker games in mind. I'd strongly recommend checking this one out.
The Gambler in GURPS builds on "Bet on It." Poker games were very much in mind when it was written. (full disclosure: this one is mine...)