It all depends on what you want to spend and how much noise you can put up with.
I have an FOP38, with a Delta on it (i.e. - loud bastard) If you are willing to put up with a lot of niose I would reccomend it a lot of sites have said it is the best and mine is keeping my t-bird nice and cool, though water will soon take that over. If you don't want too much noise the FOP38's little brother the FOP32-1 is good, they are the same heatsink just the 38 has a delta and the 32 has a slower fan (Y. S. Tech) it won't get as cool but it is still pretty good.
The FOP38 is $26 at millisec.
http://millisec.safeshopper.com/3/403.htm?949
The FOP32-1 is $20 at millisec.
http://millisec.safeshopper.com/3/342.htm?949