Hmmm... What is the one most thing that you want? I would tell you to wait and get a PS3, or Nintendo DS lite.... if you like those type of things. Or, I would get a 7900GT or 7800GTX. If you game, go with a full screen. There is no point of a widescreen, unless you watch a butt load of movies, or you edit WS movies. Get a good quality 19 or 20 inch LCD.
Personally, I would save it, or start accumulating products for a brand new computer. Everything is moving so fast now, you might as well just save it and but a better computer sometime in the future. Unless you NEED better parts. I go to school for Game Art and Design so I have a need for a good computer and Dual monitors, and all that jazz. But if you don't need it, then wait. Vista comes out early next year. HD vid cards Dirext X 10... all that crap. DDR2 w/AM2 proc's. The new intel chips soon.
Bottom Line: Thats a lot of money. Spend it wisely and get something that will last you for a long time.