I don't believe I'm in the market for a new one quite yet. This problem ONLY happens when I game, and only about once every 2-4 hours. I can't even say that because it's completely random. Sometimes I'll get it after 10 minutes of a game, sometimes I'll play for hours and not get the blackout.
Either way, this is what I'm running:
Core 2 Duo 6750
4GB 667 RAM
Windows 7 64bit
2x Samsung Spinpoint, no raid
Motherboard is a pretty cheapo part but it's never caused any problems before. I think this thing will last me at least another 1-2 years since I built it in January of 2008, and still runs everything at mostly high settings.