First you need to decide whether you want an AMD or Intel processor.... then you can expand on the platform.

For video card I would go either HD 4850 Crossfire ($400) or a single HD 4870 ($300). They will be out on June 25th. HD 4850 Crossfire looks like it will trade blows with nVidia's GTX 280 ($500 or $649, not known yet).

For CPU, going AMD I'd probably recommend you go with an AMD board that supports crossfire (790FX) and for CPU at this point I'd say a 5000+ BE. It's not the fastest, but it will overclock to 3GHz+ and it has better price-performance than the Phenoms. When 45nm Phenoms come out, you can upgrade to them.

Going Intel, the best thing you can get bang-buck wise is the E7200 for ~$130 along with a P35 motherboard (non-CF) or X38 motherboard (if you are going CF). It will hit around 4GHz with a decent cooler and at those speeds there is no game that needs more CPU power.