The 660 and 670 from Nvidia should be great but don't expect to get your hands on one too quickly. For right now you can get the reference 7870 for $329.99 on newegg and custom cooler ones for about $350. The reference 7950 is going for $379.99 on newegg also and would be worth the extra $40 over a GTX 570 imo.
Those 2 cards are really good deals at those prices if you ask me. Tom's even stated in their last best GPU for the money article that
The Radeon HD 7870 sets a new standard for what we expect from a sub-$400 GPU. With performance comparable to the GeForce GTX 580 and kissing the heels of the $450 Radeon HD 7950, this card represents one of the best high-end values we've seen in recent memory.
And that was for the 7870 at the ~$360 price point. You can now get a 7950 for sub-$400!