I don't know how much room you have in your case but I have a tiny case which uses a micro ATX board. I dropped in a ULTRA PERFORMANCE VGA COOLER and will never buy anything else. I think I had a failing heatsink or something because under very heavy loads my 9800gt would climb up to 120+ before I started to cry and shut it down (Although most games only brought the temp up to about 90C).
When I bought this it was only $18 US (thank god I bought 2 because the price is now about $30) and it brought my temps from 120+C to 55C stable. It looks nice (Blue aluminum, Copper Tubes and blue LED) and comes with smaller heat sinks to cool up to 10 smaller chips on the GPU. Also it has decent (if cheap looking) thermal grease.