Don't count out a 7800 GT just yet - over on Newegg, there's an AOpen GeFroce 7800 GT for the low, LOW price of just $289 after the mail-in rebate.
http://www.newegg.com/Product/Product.asp?Item=N82E16814135184
You'd be doing yourself a huge favor by getting a card like a 7800 GT over something less expensive - the 7800 GT is an incredible performer at incredible prices thanks to all these rebates that have been popping up for them lately. I personally guarantee that with a 7800 GT, you will be able to run every single game out there at great resolutions. With a pricetag like $289 after the rebate you just won't find a better cost versus performance ratio on any other card out there.
If you don't believe me on that one, you should. Honestly, at every on-line store I've looked at recently the 7800 GT's have been absolutely flying off the shelves and it's not hard to see why if you look at the price tags. I was lucky to snag my XFX 7800 GT from Zip Zoom Fly when I did; they're out of them now for the second time in (I believe) just over a week.
If you could extend your budget to within the range of the XFX 7800 GT then that's what I'd recommend getting for a number of reasons:
1) It comes with a free copy of Far Cry - a very, very good FPS - in the box.
2) You can get a free copy of Call of Duty 2, one of the latest and greatest FPS games, if you register the card on XFX's web site.
3) XFX's 7800 GT comes with an impressive factory overclock and a "Double Lifetime" warranty to boot. Basically, the warranty means that you get a lifetime warranty on the card, and if you sell or give it to someone else somewhere down the line then they'll get the lifetime warranty too. Always handy when it comes time to upgrade!
4) If the e-tailer you buy from ships you an Extreme Edition 7800 GT instead of the "normal" one (which seems to be happening frequently lately), you'll be pleasantly surprised to an absolutely beautiful piece of hardware. I've honestly never in my life seen a better-looking card than my EE XFX 7800 GT.
But, hey - any 7800 GT is better than no 7800 GT, I say. My advice is to go with
a 7800 GT.