I think my system might be what you're looking for...
I spent about 1500 on mine, these are the specs:
Phenom 9600 2.4Ghz Quadcore (Black Edition so OC'ing is good)
Powercolor ATI Radeon HD 3870 512MB PCS
500GB WD Caviar HDD
4GB Mushkin DDR2
GA-MA790FX-DS5 mobo
A new keyboard & mouse (generic)
22" Acer LCD (Max res. = 1680x1050)
I personally go with ATI/AMD because they offer pretty much 99% of the performance of an Intel/Nvidia loadout (Take a nice look at the new 4870 over the GT280, see the performance/price lowdown

)
at approximately half to three-quarters the cost.
I haven't gotten Crysis yet, but it can run Age of Conan on all max settings at like 40 FPS....and I haven't OC'ed it yet. My suggestion for a completely banging computer is to get 1.) Triple-channel memory 2.) The absolute newest Phenom or AMD CPU 3.) Run the new 4870 (when they come out with X2) on Crossfire 3.) Get a 15,400 RPM hard drive 4.) Get a 30" monitor that supports HDMI 5.) Get liquid nitrogen injection cooling (not really)
(This is for if the price ceiling is somewhere around 4000 dollars.)