From whatswithjeff.com: "With all the graphics card or video cards out there in the market, you might be probably lost, wondering which one should you get. For those who can afford even the most expensive card, it’s not a problem. But for those who are in a budget or even in a tight budget, you will most probably look for the “bang for the buck” graphics card or the cheapest video card that could at least play the game that you like. Below is a graphics card hierarchy chart, based on Tomshardware data, to help you decided which graphics card should you get."
I went from a 9800gx2, to a 460, to an HD6950, to an HD7950 (currently). This chart was very helpful.
The HD 7970 GHZ card is a BEAST and cheaper than a GTX680. nothing beats it except a GTX690 but that's like $700.
GTX660ti SLI is the best Nvidia config u can get. More power than a GTX680 and Cheaper (GTX 660ti are usually on sale)