The new MX series of power supplies from BFG features a modular cabling system, one 120-mm fan and one 80-mm fan that only kicks in when the temperature on the secondary heatsink is above 50º C. Let's see if the 550 W model (MX-550 or BFGI550WMXPSU) is a good product.

http://www.hardwaresecrets.com/article/665