I have a Gigabyte fan for my processor and when it was connected to it, I got temperatures in the mid 50's or so... just browsing the net and such. When it is idle, I'd be lucky to get below 50 (temps are in celsius). However, I've been looking online, and I ordered the Silent Boost K8 heatsink/fan. I've been looking online, and apparently it keeps Athlon processors extremely cool, as it is made for AMD Athlon 64 and AMD Opteron processors. Just search on google for it, and you'll find graphs and such for it that show temperature readings compared to reading from other fans. I'll let you know how it works once I hook it up.
Also, when you get a fan and heatsink, make sure you have good thermal gel. You'll probably want to get that Arctic Silver stuff. It works great I hear. I plan on borrowing some from a friend to hook up my new processor fan.