I already have a pretty good 8 month old home build computer but I am planning to make another one.
I am getting the i5 2500k for now and i will overclock it with stock voltage or higher if necessary.
I currently have an overclocked 7950 3GB Sapphire OE at 1000/1250 @ stock and sometimes to 1150/1175 @ 1.250v, I might also get a second one for crossfire once its price drops.
I am getting a normal hard drive and maybe add an ssd in the future.
I probably will get an internal dvd reader/writer drive since I already have an external bluray reader.
I am also getting 8gb 1600mhz which is 1.65v for now.
Corsair Enthusiast Series TX750 V2 750W 80PLUS Bronze Certified Power Supply --105$
Corsair Enthusiast Series TX850 V2 850W 80PLUS Bronze Certified Power Supply --130$
Corsair Professional Series Gold AX750 Fully-Modular 750 Watt 80 PLUS Gold Certified Power Supply --160$
Corsair Professional Series Gold AX850 Fully-Modular 850 Watt 80 PLUS Gold Certified Power Supply --180$
Either of the 750w power supplies are good. The AX 750 is more expensive but it's more efficient and modular. Get the one in your budget.
Do NOT get 1.65v RAM with a Sandy Bridge system. The memory controller is on the CPU itself and going over 1.5v voids the CPU warranty and can damage the chip. The best RAM for your system is 1.5v DDR3 1600 cas 9.