Your better off steering away from ATI's first and second generation cards at this time. If you absolutely want to stick with the x800 series go with a X800GTO2 and unlock it.
But it'd be a better idea to shoot for the X1600PRO, which is basically the same thing except with SM3 support and a little better around the edges.
But if you want the most bang for your buck and you want to get some serious performance as well here are some great options to look at:
6800GS, 7900GT*, X1900XT
*Note that the 7900GT is not to be released until mid March. It's going to be $300 and grant power of the current 7800GTX 256 (which costs an average MSRP of $450!). The 7800GT is a great video card for now, but since it's around the same price of the 7900GT it would be a great idea to wait for the 7900GT.