Edit: Also if you go with the SFF21F - 1600 RPM / 63.7 CFM / 28 dBA version, make sure you order 2 or more, you'll get a price break of $13.99 each, vs. $25 for just 1.
Yate's are also good. There is some debate about where to get "good ones," but Jab-Tech has them cheap and they range from low/quiet to high speed. They have 3 and 4 pin connectors on them.