You'll definitely want to install a high quality cpu heatsink for overclocking.
Here is a link to an excellent web site with a lot of useful information about cpu heatsinks: http://www.frostytech.com/top5heatsinks.cfm
There are technical reviews for each heatsink listed. You can use the embedded search engine to find information about socket specific heatsinks.
I still use an original Thermalright Ultra 120. It was one of the original if not the original tower style heatsinks. Results are outstanding for me. The newer version is the Ultra 120 Extreme. It's another good one.