(I know, kinda late but!)
Two rules of thumb:
1) the heavier the PSU, the better it is (no, really!)
2) get 80+ certified PSUs - silver will do, but if you can afford gold, go for it
You can also use a PSU calculator to figure out how much power you really need:
http://extreme.outervision.com/psucalculatorlite.jsp
As for me, I use a Silverstone 850W PSU with modular cables and 80+ silver rating. Can't remember the exact model off the top of my head, but I'm running a 2500K with crossfired 6950s plus a GT440 for PhysX and the rig has never hung on me playing either Battlefield 3 or Arkham Asylum.
Happy hunting!