I've been getting different results from all those power supply calculators out there. Which would you trust?
I want to run a Core i5 or i7 with no overclocking, Zotac Amp GTX 680, 3.5" 7200rpm HD, 2.5" SSD, 2x4GB G.Skill ECO 1.35v DDR3-1600, and several USB peripherals (USB sound card among them).
Extreme Power Supply Calculator has always been accurate enough for my needs:
http://extreme.outervision.com/psucalculator.jsp
A 450W sfx psu is easily enough for your system.