I've already gone over this, but to summarise.

To build a good stable system that offers plenty of future opportunity to upgrade, in order of importance

• Motherboard: chipset is most important, followed by quality of power regulation circuitry (one of the more expensive elements of motherboard design).
• Power Supply Unit: not wattage, but quality of ampere supply. This will mostly guarantee forward compatibility with graphics cards, as it's not atypical for a high end graphics solution to consume as much as everything else in the system put together
• Central Processing Unit. A good choice of CPU will carry your system through several generations of upgrades. There's always a sweet spot in the CPU market, where you get a pretty high end unit without buying into the ultra high end.
• Graphics. It's nearly pointless buying the flagship part because it will be replaced in 6~9 months and depreciate in value rapidly. The performance gap between flagship product and second level product will close over time, so you don't even buy a longer life cycle.