If you're planning on buying a compt. Do a custom one, for your need!
Here's my spec and I can run any game at ultra or best graph allowed on the game, Bf3(most needed on computer power on market)/Crysis/Sims3/SimCity/FarCry3 etc. Without any issues on it :
Tower (yes you got to buy a tower) : ThermalTake V9 Black Edition. Google it, i've got the one without the ''window'' on the side

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Processor : Intel(R) Core(TM) i5-3570 CPU 3.40 ghz (I'm NOT doing overclocking)
MemoryDDR (RAM) : 16 go
OS: windows 8 64bit
Local Space : 500go (not need much for now)
Graphique card : Nvidia Geforce GtX 660
Note to go check with an expert, you have to get the good powersupply, etc etc. Just giving my spec, there's more to buy then only these ^^.
Enjoy asking question about what is needed for wich use etc.
Some question might be over my knowledge, sorry. Still, I will try to help you out

Nutz-