Goddamn, make 21 card twist!! that so rules...
Oh, how about a game where you roll the dice and try to roll a randomly generated number. if you win, you win double $, lose... well, you lose $ Simple, but addictive
You could probably make some kind of race game you can bet on, like horses or dogs. You could give the racers different stats like speed and stanima, and there could be odds on who'll win depending on their stats. Shouldn't be too difficult to make.
A roulette game wouldn't be to hard to make anyway. It's pretty much a random number generator. You'd just have to do calculations on how much you make from what you bet on, Pair, Impair, Rouge etc. If you can bother making BlackJack, you can easily do roulette.
This is a sweet idea dude, a casino simulator. Take a bit of time on it and you'll have an original click epic on your hands.