pretty much whatever he said, just get one with a copper plate, and heatpipes, doesn't matter bout the fins too much but aluminum cools faster than steel and is lighter than copper. and the cheapest you can pay. if you are serious about your overclocking and cooling you're going to lap it anyway. get a cheap one that has a mounting plate, lap the shit out of that motherfucker and then watch your temps fall.
also if you aren't that serious about your overclocking get a zalman, they are worth the price, but don't overpay. don't pay more than $5-10 over whatever other brand is second cheapest to zalman. zalman = the best if you want cool and don't mind paying a little extra. but if you are going to lap then just get a cheap one.