What will you be using this build for? Remember that an i7 is overkill for gaming, and the performance increase from a i5-3570K isn't worth the price if that's your most intensive use case.
If you don't plan on changing the GPU, a 500-600W PSU is perfectly adequate. 700W-800W is recommended if you do plan on a top tier card. Go for Corsair, OCZ, SeaSonic or Thermaltake.
HDD: Go for a Seagate Barracuda. Cheapest on the market and reputable brand.
Seconding the 3770K -> 3570K and 7850 -> 7950. Much more bang for your buck with that configuration. (Though remember to get one with a non-reference cooler like a MSI Twin Frozr or Gigabyte Windforce if you plan on overclocking Radeon cards in general. Their reference blowers are noisy and don't cool very well.)