I ended up getting one of these last year when my stock fan starting making funky noises. Besides making 1/3 the noise of the stock fan, the "at rest" temperature is about 1/2 of what it was with the stock fan. Even after a torture test, the temperature was still a few degrees less than what the stock fan kept it at while "at rest" !!
Only downside is that it does take up another slot. Didn't matter to me, as I always try to keep the slot next to the graphics card empty for cooling reasons.
Jase03: This replaces your stock fan/heat sink.