Well, I guess it depends on:
A. What speed grade of Athlon 64 you have, or plan on buying.
B. What do you plan to do with it.
The cooling requirements for an 104W FX-55 are slightly different from those of a 2.0 GHz one. Also the answer is very different if you want to overclock, compared to someone just wanting silence.
Also, having a fan controller isn't always the answer. Going under a certain speed, which is what a fan controller allows you to, might not cool well enough any more.
That said, as I've posted several times before, personally I'm using a ThermalTake K8 SilentBoost on my 2.0 GHz 3200+ (1 MB cache), with the fan replaced with a 12 dBA Past fan. All copper, lots of fins (hence lots of surface), and seems to do surprisingly well with a slow silent 80mm fan.
But then I fit in the niche which values silence over overclocking potential. Whether that's what you seek too, that's another question.
Downside, you do have to swap the fan on it to get any silence. The numbers for the default fan on it were obviously pulled out of the ass by a marketroid, rather than measured. It's nowhere near 21 dBA, but _at_ _least_ 30 dBA, probably more, and the airflow is probably nowhere near the one they claim either.