I recently changed my CPU cooler to this one:
http://www.newegg.com/app/ViewProduc...106-037&depa=0
Reasonable price, REALLY cool and extremely quiet (compared to the AMD OE unit I replaced). In my mid-tower case, I had to unbolt the power supply and slide it out of the way while I installed the heatsink. This only took a minute and made the whole job quite easy. (Bought mine at Micro Center, but price was comparable)