3800+, ocz ram, 7900gt, so far EXCELLENT choices.
the asus a8n32 is one of the best SLI mobos out there, i donno what that other guy was talking about. DFI is also a good brand. but since you don't intend on getting SLI, just get a single slot mobo and save some money.
as for power supply, get this:
your 7900gt requires:
Minimum of a 400 Watt power supply.
(Minimum recommended power supply with +12 Volt current rating of 20 Amp Amps.)
Minimum 500 Watt for SLI mode system.
(Minimum recommended power supply with +12 Volt current rating of 28 Amp Amps.)
An available 6 pin PCI-E power connector (hard drive power dongle to PCI-E 6 pin adapter included with card)
so i high quality, affordable 450watt psu like the one i linked should be good enough for your setup.