I highly recommend building your own, even if you have no experience doing so.
Edit: There's a wealth of information available if you don't. A lot of it is simply making sure you get the right type of parts, and are able to slide a rectangle into a rectangular hole. If you've got trouble I'm sure a lot of us can lend a hand
RoG Crossfire V: ~$300
i7 3770k: ~$300
GTX 650: ~$150
So, $750, and you still have enough to dump into whatever size HDD, RAM, you want.
This will be more than enough to run most games without a hitch.
I'm currently running a variation of this (although way more costly).
The 3770k is a great processor. It's 3.5 GHz (not counting turbo) out of the box. Right now I've got mine running nearly 24/7 at 4.9 GHz. I've gone higher, and would be able to sustain it, but 4.9 is enough for me (at the moment anyway) lol.
The 3770k processor is great. I do some game development, and heavily multi-task when I do. I see no slowdown regardless of how many programs I've got open - and it's usually whatever engine I'm using, 3D modelling program, Photoshop, various other programs, and many times 20+ tabs in firefox.
This combined with a GTX 680 and I smoke everything FPS-wise. If you wanted you could make the jump right away, if not and you've got spare cash later on and aren't really like your framerate the RoG motherboards have a lot of overclocking capabilities, and allow up to quad-sli/crossfire.
If you really want to game, I can't recommend a serious PC setup enough.
Edited by ChipNinja#1794 on 3/21/2013 7:14 PM PDT