Socket 939 heatsinks. Cheap, the best in it's price class: <a target=_blank class=ftalternatingbarlinklarge href="http://www.newegg.com/Product/Product.asp?Item=N82E16835185125">Arctic Cooling Freezer 64
</a>. Better, and also easy to install:
Zalman 9500. And slightly better that both of those, but not all that easy to install:
Scythe Ninja <that one comes without a fan, so you'll need to order a 120mm fan with it. And this one's slightly better:
Scythe Infinity.
There are others, but those are really the best in their price range (at least that come to mind right now). Oh, all of the Thermalright's that use a 120mm fan, and have heatpipe's are good, also.