Hmm... For $150US, I would probably reccomend the Radeon 9600XT. As has been said, it's a highly under-rated card, thanks to the fact that it came a few weeks after the far more powerful 9800XT. My brother's computer uses a 9600XT, with an old (Thorghoubred, not Barton!) Athlon XP 2400+, and can run UT2k4's benchmarks at 800x600, with full x6 AA and x16 AF, and get ~50-60 fps. It's easily more powerful than the 9800SE and 9800 Standard, and perhaps only a relatively small gap (40%, small for computer technology) less than the 9800Pro. $150US should be enough to get the 256MB version, Though from
NewEgg, that's the price for a new bulk OEM card, which means the smaller box, and no Half-Life 2 Bronze voucher for Steam. (which I would simply recommend getting the boxed version anyway, as then you don't have to wait 24 hours to download it, and can install if you don't have any form of broadband)