I've got a Phenom II x4 955 black no overclocking, and the stock heatsink.
Well it has started to get REALLY loud, so I'm trying to find the quietest heatsink that will work with it. I thought about going fanless but I don't think that's realistic (correct me if I'm wrong please).
Depends on how much money you want to spend. For both of my current Intel LGA 775 PCs I have a Tuniq Tower installed. I also replaced the fans that came with Yate Loon fans. Total cost was probably around $50 - $55 for each PC.
The Tuniq Tower can even passively my Intel C2D E6600 (Conroe) at stock speed. According to Core Temp it typically gets to about 77C with a 100% load; TjMax is 95C if I am not mistaken. It normally does not reach 100% load since I just use that particular PC to watch movies.
Here's a link to Tuniq's current heatsink which is compatible with AM2+ and AM3. It is $65 though.