Xoxide has some good stuff for that very purpose. I can pretty much say that all of this stuff is probably better than the stock HSF you would get anyways.
Directron's is pretty good as well, though probably not as deep.
1CoolPC, while incredibly plain/ugly in it's design, is also a decent site.
You could always check out
Pricewatch, but approach with caution, and use
Resellerratings in conjunction with any searches that Pricewatch might lead you to. If they ain't got a high rating (7 and above), don't do it.