If you want to future proof a PSU you need to consider the amperage as well as the wattage. With Nvidia and Ati both approaching the various PSU companies about the increased energy demands of their GPUs, you need to look at PSUs with multiple rail systems that also present a good healthy amperage. Antec, OCZ, Mushkin, Silverstone and Enermax all have good products. Don't get something with less than a 17amp average over each rail.
For instance, I have a XFX 7900 GTX Extreme that I overclocked and my FSP 700 couldn't handle it because, as their technical support informed me, it had too weak an amperage (15 amps) across its rails. It's an awesome PSU and could power your 7800 GTX in SLI but beyond that, it had issues with. So I replaced it with a Silverstone 750 and it handled the GPU nicely.
I have a large energy demand on my system:
Presler 955 3.46
Abit AW8D
2GB DDR2 800
XFX 7900 GTX Extreme
2 Raptors HDDs
320 WD Sata HDD
Creative XFI Fatality (with drive bay unit)
(11) 120mm fans (8 are on rads mounted externally, 2 are LED 1 intake 1 outtake for airflow, 1 for drive cage)
(4) 40mm fans (modded Abit Voltage regulator heatsinks)
Swiftech 655 Water pump
Relay Switch
(2) DVD R/RW Drives
56-1 card reader
floppy drive
Dual cold cathode light
Bay drive voltage adjuster for CPU Peltier Waterblock
(assorted USB devices)
all powered by a SILVERSTONE SST-ST75ZF 750