The Profession(Gambler) option is what I use.
From the size of the town (from hamlet to metropolis) I set an available 'pool' - the value of the monies the player may win on any given night. He sets his 'bet amount' to whatever he wants (I don't tell him the pool size).
I set a DC to whatever I feel the 'difficulty' of the town is (as far as bar betting, and the like) - organized 'casino' types are harder.
He rolls above that DC and wins 10% of the pool per point, or loses 10% of his 'bet' if under. Breaking even is meeting the DC.
Example:
Deacon is in Rielson, a small hamlet, and decides to involve himself in the local gaming scene. Rielson has a 'pool' of 3 gold. (big winnings for a small town!) Deacon has a Int of 15 and a Profession rank of 6, for a total modifier of 9. The DC for this hamlet is 10 - these are amatuers. Deacon rolls a 16 - that's 60% of the pool. He walks out with 18 silver.
Later on, Deacon makes it back to Dhunraven - there's a lot of trade through this town from the northern tribal groups to the southern kingdoms, and that brings money and people willing to lose it. I set the DC at 25. Deacon rolls a 13 on the night - ouch! He's lost 120% of his 'bet'. (things got a little out of hand)
As far as 'quick', yes, this system is. One roll and 'bam!'. It's fun depending on the player. He wants his character (a priest, BTW) to go hit the local scene, drink, and gamble, he does so. We combine that 'roleplaying' bit with Gather Info checks and whatnot, the usual things players do when 'downtown' during an adventure, and the Prof(Gambler) finishes the night - big losings gets him invited back for more (and perhaps some bonus on Gather Info, from one gambler to another) and big winnings may get him 'uninvited'. We've all seen the Vegas movies
He does tithe.

I'm not really sure of the validity of the system, but it doesn't really matter to me, at least - the winnings are 'small' compared to the winnings from gambling your life in a dungeon. It's just a little flavor.
Koewn