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.
AMD Athlon 64 X2 4400+ / DFI Lanparty UT NF4 SLI-DR Expert NVIDIA Socket 939 / FX GeForce 7800 GT 256MB GDDR3 / 2x1GB of G.Skill PC4000 DDR500 184.108.40.206 F1-4000USU2 / 19" Kingston LCD / 550 W ULTRA X-2 PSU / JBL 5.1 / PS CS2.0 / 120 G 7200RPM I also have an Olympus Evolt E-500 digital camera and 9" WS portable DVD player.