The stock AMD heatsink isn't bad, I've heard decent things about the Thermaltake SilentBoost, the Zalman CNPS 7000\7700 series (it's what I'll be using on my A64 system) and the Thermalright XP-120 (if it fits your motherboard) and XP-90 are all very good solutions that will cool as well or better than the Asus and are cheaper. Note that the Thermalright heatsinks require you to add a fan of your choice (Panaflo L1A\M1A is popular).