If you want an excellent product I will recommend the Noctua NH-D14 Link not cheap but is capable of great performance
Hey, thanx peeps - lots of references to look up and check. Great supportive forum - much appreciated.
Noctua NH-D14 Check out Xbit Lab's Review of the Noctua NH-D14 I expect that it'll be the new champion of air coolers for a little while. It's what I'm going to use for my next i7-860 build and would certainly work for i7-920 overclocking. Also take a look at this for ideas if you can make room in your case.