i5 2500k w/ aftermarket Cooler or 955+ amd MOBO depending on socket but id go asus myself
6gb of ram will power any game even BF3 at ultra but 16gb isnt expensive even if you go ripjaw or corsair veng
Nvidia 460 radeon 6850 nvidia 570 and 580 aswell as Radeon 6970 are all topnotch
PSU to support higher end cards id go no less than 600w and NAMEBRAND p.s. get a psu tester so u dont fry your components
7200rpm or higher HDD or an SSD
DVD R/W for os install or bluray budget dependant
Case will good airflow cant go wrong w. Coolermaster but most case's with adequate cooling and cable management will work fine
add 1 computer geek to OC your i5 to atleast 4.0ghz 4.5 if possible 5.0 if you can afford the cooling! however not all will make it to 5.0 but pretty much all will goto 4.5 still a risk factor so get a geek who knows what they are doing to do it.
1920x1080 monitor or higher and WOOSH into la la land at most games running 60+ on full settings
NOTE1: Prices for each product are estimates and might not be correct. NOTE2: Some parts (like for example the case) can be swapped out based on personal preference.
I'd also recommend to check out Chaud's "Setup of the Month". They are very good starting points when looking at computer hardware. It's also advisable to give a budget.