Prophet may not be an ATI guy, but I'm just going to jump in and vouch for the Radeon HD 4850. It's got ridiculous amounts of power considering the $140-150 price range (after rebate), even beating the 9800GTX+ in certain benchmarks (ATI's always had the upper hand when it comes to anti-aliasing), and the initial complaints of heat are no longer an issue now that dual-slot versions have been released. That's the key thing to remember, though - get one with a dual-slot cooler, or else you'll be looking at 70-85C idle temperatures.
As sort of a side-perk, it comes with an onboard 7.1 sound card, which'll be invaluable if you're into home theater. The 9800GTX+'s gimmick seems to be the onboard PhysX processor, so if you plan on playing games that support physics acceleration (there aren't a whole lot) it might be the card for you.