Thermalright Ultra 90 - $19.99 at SVC.

Great Heatsink at a good price.
I order from these guys all the time, as they are one of the few that dont rip us alaskans off on shipping costs. always been happy with them so far.
this heatsinks usually $40 or close.

http://svc.com/ultra-90-775.html

already been posted but good deal, from a great company btw, regardless. Also the K8 version is 14.99 or something like that.