See, I don't trust PSU calculators, and would prefer to ask you guys.
I'm going to be building my first rig shortly, which will consist of the followin' parts:
Sapphire HD7870 2GB
8GB Crucial Ballistix Smart Tracer RAM
Western Digital Caviar Blue 1TB
FX6300 Black Edition 6 Core
Will a Corsair 500w PSU be sufficient, or will a OCZ ZS Series 650w be reliable enough?
500w should be sufficient but it'd be operating near the power supply's max load. If you want a little head room for future upgrades I'd go with the 650w however as I said a Corsair 500w psu would be sufficient.