I using the Taisol CGK74209, with a Delta 38CFM fan, $35. Works great, have a 800Mhz tbird going at 1Gig and stays at about 43 degrees celcius. It's a little noisier than I would like though. If your very concerned about noise, I would suggest going with a smaller size fan or putting some sound absorbing material in your case.
Here's a good site for fans and etc.
Inflow Direct