For a relative:

Intel Desktop Board DP55KG
4x Seagate 1.5TB
1x WD 500Gb
Samsung DVD-RW
HD 5770

OCZ ModXStream Pro 500W ($50 after rebate)
OCZ ZS Series 750W ($65 after rebate)
XFX Core Edition PRO650W ($79 after rebate + Dirt3 Game coupon)
SeaSonic S12II 620 ($85)
CORSAIR Professional Series HX650 ($110 after rebate)
CORSAIR Professional Series Gold AX650 ($130 after rebate)

Was using an Ultra 550W that recently died. Modular or not makes no difference, and no plans for expansion for quite some time other than possibly buying a GTX 570.

Spec the PSU based on the upgrade to the GTX 570; 35A on the 12V rail. The OCZ ModXstream has a total of 36A available on the 12V rail and is sufficient for your build. If you want to pay a little bit more for a better quality PSU, then the ZS is a step up; I would consider it or the Seasonic S12II-520W (40A on the 12V rails).


Seasonic S12: II
Corsair AX650: I

So between the Seasonic and the XFX, which would be better? I personally think they are about equal. Also, the relative is looking at a GTX 480 now instead, after seeing that I bought one. I think that elimates the 500W, but does it eliminate anything else?