I have a 2x 470's and a Coolermaster GX750watt PSU along side:
4 HDD's (80Gb, 250GB, 500GB and a 1.5TB)
Blu-Ray DVD Player
Couple of USB's plugged in (Mouse, K/board, Printer, external HDD, Joystick/Xbox Gamepad)
(Main Specs in my sig)
Has been running now over a year, no stutters, nothing... Very confident and happy with it. People said it'll fall over at the first hurdle, blow it ruin your system within weeks, over a year later........
Would even go as far as to say its on average on about 15-20 hours a day aswell..
I wouldn't go for anything less, but to be honest, I wouldn't spend double the amount on a PSU for the same power, i.e. this Coolermaster cost me £100, a corsair with the same power was £220.. and had less connectors..
Im not saying get an unknown make for £20, but something quite decent is sufficient (in my experience and view)