this is the quietest 120mm i've ever heard of.. but with CFM's in the 40's (compare to 150 for ones that sound like blenders) it's not real powerful.
I've heard good things about papst fans. Also, panaflo is a quality brand for low-noise fans. Both cost more than $10.
You can get these fans and others at www.Directron.com (or do a froogle search for the model number/name). The papst is ~$18 and the panaflo is ~$14 i think.
There was a nice site that had some others but I forgot to bookmark it and can't find it now. Do some googling there are some other fans that might be cheaper.