I'm running two S3's of a FSP Aurum PRO Series 1000W Modular PSU, which gets a generally good review by Jonny Guru (http://www.jonnyguru.com/modules.php?name=NDReviews&op=Story4&reid=292 is the hot performance stats)

I've also got another two S3's, each running off a FSP Raider 650W, with an adapter cable to use the EATX 8-pin CPU power lead as well as the PCIe 6-pin power lead.