I'll just copy-paste what I just typed in another thread:
From the X1800GTO review I read on XBitlabs.com some time back, I clearly remember:
The 7600GT was much better & cheaper than the X1800GTO.
The 7600GT will play any game at Maximum settings, 1024x768, 4XAA, 16XAF silky smooth.
Less demanding games will easily allow you to retain the Max settings & IQ and bump the resolution up to 1280x1024.
Older games (Doom 3, Half-Life 2 etc.) might even go up to 1600x1200 with the same settings.
Oblivion is probably the only game which can't be turned up to the max and blazed through: I'm sure you can find a decent compromise between res/IQ/performance.
At ~$140 (after MIR), the 7600GT is a no-brainer if you can afford it - maximum returns for your investment.
The next speed-bump would be a Sapphire X1800XT 256MB (Retail) that is $230 after MIR, on Newegg. The same money can get you a stock-clocked eVGA 7900GT (after MIR) on Newegg.
The general consensus on these boards is: 7900GT OC's like a dream, takes a single slot, uses less power and has equal or better performance in most games which makes it a better choice. The X1800XT has HDR+AA capability and is still a formidable choice, so make sure you look up a recent 7900GT review where the two are compared head-to-head. Driver releases sometimes help one card outdo the other.