A investment into a decent heatsink and fan is a really good idea for AMD's or Intel's...period. HSF's don't cost that much for really good ones. $25 or so can get you a top HSF. That's not much when you consider what you are paying for a CPU and a mobo.
There are some HSF's that are a bit pricey, like the MC462 ($70 or so), but this HSF is really only for anyone into extreme overclocking.
Some of the better HSF's are made by Cooler Master, Globalwin, Vantec and Arkua just to name a few.
I personally have the Arkua 7228 on my AMD XP2100 and it ran around 40-42 C under heavy 3D load. I paid $24.99 for this HSF at the Heatsink Factory (
http://www.heatsinkfactory.com).
Yes, it does have a loud, screaming Delta 60mm fan on it, but I remedied that by replacing it with a 92mm fan using an adaptor. The 92mm fan moves more air and is less than half as loud. I now get temps around 39-40 C.
