Noctua NF-A4x20 5V PWM, Premium Quiet Fan, 4-Pin, 5V Version (40x20mm, Brown)

Installed easily with screws I had laying around. Turns on when its needed and off when its not. The only complaint is the rubber corners on the top of the fan eventually rubbed off and one day one of them jammed the fan blade up and almost overheated my nano. But I took the rest off and its fine now.

I am really impressed with the amount of additional cables, connectors, and mounting options provided. I ordered the fan to place inside of a fursuit (costume) head. It is very quiet, if even one person is talking you cannot hear it running. The air flow is low, but it is constant and hands free so that is very nice. I thought it might be much louder than it was which is why I ordered the PWM version. Since it is *so* quiet theres no reason to not let it spin at full speed unless your application is severely power limited.