I haven't found a lot of quiet ones, but I did buy my quietest one on eBay. Also, go to CompUSA and look at the computer fans. You have to attach a power cord using a cut off extension cord, but that's really easy. You can them much cheaper this way than through a pet store. My LFS (which I like) wanted $35 for one fan, I could get the same fan at CompUSA for about $12. Make sure to run any fans pushing air into the hood, otherwise, the computer fan is not adjusted to the humidity and atmosphere of the tank air running through it.
