Thermalright was one of the first manufacturers to get it right. Their debut heatsink, the SK6, was made entirely of copper and appealed to the majority of the AMD overclocking crowd, mostly out of a simple and effective design. The SK6 certainly wasn't a budget minded heatsink and i can vaguely remember that less than a year ago they were going for around $40. The SK6 rated high not only among enthusiasts, but with hardware review sites as well, mostly due to the fact that some of the best heatsinks from manufacturers like Swiftech, Kanie, Alpha, and others were actually at the same level or worse than the SK6. For the est. price of $40 you really couldn't have a better performing HSF at that time.
Now times have changed, HSF manufacturers are looking more and more into what made the SK6 such a success. A simple search on the internet for AMD heatsinks will leave you confused with what to buy not to mention all the names for the same design that made Thermalright so successful. As for as this writers opinion there are pretty much three categories of heatsinks on the market today...
Review Link : ClubOverclocker