Re: my first build
As ssc456 said, a 500 watt PSU is sufficient for the hardware you listed, as long as it is a high quality product.
Also, take into consideration any upgrades for the future. For instance, if you decided to add another 5870 in the future for Xfire, the 500 watt supply would not be sufficient.
HAF 932 Advanced / Corsair AX1200 / Asus Rampage IV Extreme / i7-3930K / H100 Cooling 4x120mm
16GB Corsair DDR3 / GTX 580x2 SLI + GTX 460 PhysX / SSDs Mushkin 240GB, Crucial 256GB, Crucial 512GB