Tomshardware has shown that anything from a dual core pentium upwards can play modern games and run graphics cards up to a 9600gt pretty well.
It pretty much shows that all you need for gaming is a decent Core2 or AMD X2-3-4 processor and that your money is best spent on the graphics and you can skimp on the processor.
http://www.tomshardware.com/reviews/cpu-gpu-upgrade,1928.html
Pretty much you can get whatever is cheap and has a decent upgrade path.
For example, AM2+ Motherboard with an AMD X2 4200+ then you can upgrade it to a Phenom X3-X4 45nm if you want.
So for value for money - Skimp on the CPU and spend that money wisely on a graphics card.
Lastly, the new generation of cards is 1-2 months away so I suggest anyone not getting an EVGA card with stepup to skip the highend 9800gtx-9800gx2 and look to get either a radeon 4870 (Or X2) or the new Nvidia GTX and GTS cards in a couple of months. It looks like quite a jump so hold off if you can.
Tease.
