Heatsinks that fit onto existing AM3 Board mounts for 955be

Here is one that won't require the removal of your mobo.
http://www.newegg.com/Product/Product.aspx?Item=N82E168...

This one does but is much better.
http://www.newegg.com/Product/Product.aspx?Item=N82E168...

Or if you happen to have an older s939 Opteron heatsink lying
around you could use it.

The CPU/sink is the first thing you install when you are building. If you want to install a sink that requires no backplate you will have to settle for a mediocre cooler.

The only cooler that I can recommend if the freezer 7 as long as you do not go crazy with the overclocks. The freezer 7 is overpriced for what you get so choose wisely!

I strongly recommend that you remove the board and install a cooler that requires a backplate unless you will be running your CPU at no more than 3.7/3.8Ghz.

http://www.frostytech.com/top5heatsinks.cfm?id=QeeVTha7

Agree backplate coolers are better. And that one linked above (Cooler Master plus 212) is worth every penny.

Currently I'm running my amd 955 at 3.8 ghz and it runs idle at 27c and on 100% load on all 4 cores, it's like 40-41c.

THe CoolerMaster TX3 would also work and does a decent job of cooling though it is a 92mm design instead of the 120mm design on the 212+ so isn't quite as good at higher OC's --- and it does not require the backplate.