I noticed you have an AMD system. A cpu heatsink sometimes produces different cooling results for AMD and Intel cpu's.
The Frosty Tech web site mentioned by tecmo34 is a very good site with a lot of useful information about heatsinks that can help you make an informed decision. Here is a link to their current top rated heatsinks:http://www.frostytech.com/top5heatsinks.cfm
Scroll down the page to see the AMD list.