I used a 1000W Ultra X3, because I got it cheap ($324 with an AMD X64 FX62 2.8GHz CPU). This to run that CPU, one HD, one optical, an 8600GTS, sound card, four fans and a Zalman.
No, I'm not lamenting my stupidity.
It doesn't matter what you want on the comp now, what do you think you'll want on the computer in a year? Two years? Me, I want to have an SLI'd pair of G92'd 8800GTS's and a Raptor HD by summer. Lord knows what I'll want six months after that, and Lord knows what the power requirements will be by then.
My point is...shop within your budget, but remember that you won't want to plunk down another $100 a year from now when your power supply won't handle your next planned mod.
Or when that happens, you could just hack out two 5" drive bays and wedge a 250W PSU to power your new gleaming video card. Laugh not, I have seen it done.