The Dark Knight is the best cooler for less than $60, it really is amazing. It can take 1.6v from a Phenom II and keep temps under 75c, that's borderline watercooling performance. The only thing to keep in mind is that it is odd to install, so don't be impatient. You may need to reinstall it several times until you can find a technique that produces very good temps.
Phenom II 940 @ 4.1 Ghz 1.55v + Dark Knight = 38c idle/ 68c load.
I would list what I got off of it with my i7 920, but I have an extremely poor overclocker so I'll just keep that to myself...