Odd, I just built a machine with the Athlon II X4 640, and for the first time in a long time used the stock cooler in a build. Personally I find the fan to be silent, especially compared to those copper heat pipe fans that come with the Black Edition processors.
I've also got an Athlon II X4 630 running the Hyper TX3 already linked above, great little heatsink, only noisy under full load running 3.5Ghz.
Well my case is a NZXT M59 which is pretty open.
My problem isn't that stock is so loud but I often just use my computer for surfing so I don't have any headphones on and when i turn off my computer the difference is really obvious.