A few to choose from here:

256MB XFX nVidia 6800XT (8 pipes, 350/1000) = (link)
512MB XFX nVidia 7600GS (12 pipes, 400/533) = (link)

I've never used ATI cards (I prefer nVidia, as above), but this is in the price-range you wanted if you'd prefer to stick with ATI:

512MB Sapphire Radeon X1600Pro (12 pipes, 500/800) = (link)