I agree with Bassmanic. The ATi cards are cheaper, very good, less fan noise (not all cards), a lot cooler temperatures and requires a lot less power consumption (PSU).
Are you looking for a card to use for all new high-end games for the next year or so and to play TDU2 at max (++), then go for HD5870 (or maybe crossfire). Do you want something cheaper (but still suprisingly good and supports Dx11. I think the cards are undervalued), then go for HD5450, 2x HD4850 ($230), HD5750 or 2x HD5750 ($260). Make sure you have a PSU to match your hardware (watts).
The new Fermi cards by Nvidia are also good. The downside to Fermi is that they uses a lot more PSU and they get very hot. In another hand, drivers just released has improved things a lot. Some says up to 20% performance for some games. That's much. If people wait another couple of months then I think the Fermi cards will improve even more, especially at PSU and heat wise.