Yep with Core i7 pricing at the moment you should go for high end, 4870x2 or GTX295.
If you're not looking for a high end system you can cut your cost in half and get E8500, 6 gigs of generic ram, much much cheaper motherboard and a 4870 or GTX260.
You'll get the whole system for quarter of the price of an alienware (monitor included) and it will still run every game available today with playable framerates.