Some users have recently had their accounts hijacked. It seems that the now defunct EVGA forums might have compromised your password there and seems many are using the same PW here. We would suggest you UPDATE YOUR PASSWORD and TURN ON 2FA for your account here to further secure it. None of the compromised accounts had 2FA turned on.
Once you have enabled 2FA, your account will be updated soon to show a badge, letting other members know that you use 2FA to protect your account. This should be beneficial for everyone that uses FSFT.
While the power reqs for your current rig don't seem too high, if you're truly trying to future proof yourself and have a propensity for sli/xfire, then I'd pick up something around 750+. If you dont plan on going dual gpu in your new build or at any point with this psu, you could ratchet down a bit. As has been discussed in other threads, go with quality on psu - brands I always look to are corsair and seasonic, but I've heard good things on some antecs, xfx blacks, as well as silverstone. Jonnyguru is a great site to check for reviews and psu discussion.
In any case, a good quality psu can last you through multiple builds if you allow enough overhead.
Why do people keep planning out half ass upgrades. If you are going to get everything new except the GPU, hold off till you have the funds and go all in. That 8800 dramatically kill the fun factor. Plenty of options in the $100-200 market. Also rather than 4-5 1tb drives how about a SSD and a 1tb drive? You could get away with a sub $150 64GB SSD for the OS partition and apps. Install steam and your games on the 1tb.
Back to the OP. Anything above 520watts should be more than enough. 750 would only be needed for sli or cf.
Don't cheap out on your PSU. You'll regret it in the long run. A Corsair TX650 or HX650 will be really nice, and the HX is modular so you can remove cables and whatnot, allowing for better airflow.
I personally wouldn't go for a CX power supply unless it was dirt cheap (like a CX430 for $17 AR). Reason being mediocre efficiency (barely 80+), and decent quality. There's better options out there for the same price, like the Antec Truepower New, or Corsair's TX V2 series.
What kind of GPU will you upgrade to? Mid-range (GTX 460/HD6850/6870 level), or high end (GTX 570, HD6950 level)? Because those are two different power consumption levels. A dual 580/6970 system would require a 750 watt at least, while dual 460's and 6870's can get away with a 650 watt power supply.
I do have the CX430, and Corsair's new line of CX power supplies are cheaper in general. The older CX400 was a better design than the CX430. I'm not saying they're bad, but there are better options available.
Dual 460's or 6870's can probably be easily handled by a good 650 watt power supply.