$1000 would give you a VERY strong system.
Go over to cyberpower. google them, also use the cyberpower foum on this site,
Look at intel i5 based builds. The i5 will be i5-2300, i5-2400, i5-2500, i5-2500k. You want any of these, but should not be paying a big premium for any of them. Hold off overclocking until you can afford to fry a system -- i.e. don't do it.
Look for a video card that is HD6850 or better. This article recommends cards, but more important -- the last page compares all cards so you can see which cards are teh same as HD6850 or better. http://www.tomshardware.com/reviews/fastest-graphics-card-radeon-geforce,3085-3.html
I think you can find a great system for less than $1000. Try starting with a system with i5-2500K and step down to i5-2400, step down on MB to H61 no z68. Step up to hd6850 video = $900.
Aside, See if you can get the change from $1000 put in a STEAM account for you (do you use STEAM, if not take a look. It beats the heck out of needing DVDs to play games and trying to remember where you put keys when you change PCS or wipe out a hard drive).
EDIT: I picked intel i5 because 2 years from now you can slop in a new video card and play this system for another 2 years. IF you need to save $$ now, go to intel i3-2300 based system. That should knock another few hundred off price and still be strong enough to drive the 6850 for gameplay. It just won't have as long a life before it gets too slow. Avoid the new high end AMD 'bulldozer' based systems -- they have a few performance bugs to work out before you want to go there.
EDIT 2: I see your budget went down from $1000 to $800. Go to the cyberpower forum adn ask over there what systems they recomend at that pricepoint.