It would depend on how much room is in your case, but right now this Xigmatek direct-touch heatpipe cooler
is on sale for $12.99 after rebate at GougeEgg, and looks like a great deal as long as you don't mind mail-in rebates. If you don't like the push-pins you'll have to get the bolt-through mounting bracket, though. These direct-touch heatpipe Xigmateks have the performance of the high-end (>$50.00) coolers and are quite a bit cheaper. They offer monster overclocking headroom if you're into that kind of thing.