Depends what you want to spend really. I have just purchased a Geforce 570GTX Graphics card, I think it's a good price and it's not a mile behind the Geforce 580GTX in terms of performance. Anyways, it plays all my games on high settings, except for the game Metro. However, I am not willing to spend big just to get good performance out of a handful of games. If you want to spend big there is always the Geforce 590GTX, but I think it's to expensive for what it is.
BTW - 24 Gig for games is a bit much, or are you doing video editing and that?