From what I've been reading, the Xigmatek S1283 is the best air cooler currently available, and quite reasonable at $36.99 on NewEgg with free shipping.http://www.newegg.com/Product/Product.aspx?Item=N82E16835233003&Tpk=S1283
It is a push-pin style cooler but you can always buy a backplate kit for $6-8 dollars more if you want to go that route.
The new Sunbeam Core Contact is supposed to be even better, but I haven't found anywhere that actually has them on sale yet. The Xigmatek S1284 is coming out in July but the benchmarks I've seen actually rate it a little lower than its predecessor, though nicer-looking. The OCZ Vendetta 2 is also supposed to be very good but is much pricier.