Well I would not recommend a Intel set up under $1000, so I will give you some AMD stuff...
First the Motherboard:
http://www.tigerdirect.com/applications/SearchTools/item-details.asp?EdpNo=1963472&CatId=7248
Its a MSI with at AM3+ socket, so you will be able to get a lot of performance out of it...
$94.99 ($15 mail in rebate)
Next a good CPU:
http://www.tigerdirect.com/applications/SearchTools/item-details.asp?EdpNo=1372438&CatId=7341
Quad Core 3.6Ghz, this will handel any game you throw at it... if you really want a performance boost with this processor, use Windows 8.
#109.99
Some RAM:
http://www.tigerdirect.com/applications/SearchTools/item-details.asp?EdpNo=1818722&CatId=4534
This is some fairly high end RAM. Its made by Patriot so its good stuff.
$58.99
Video Card:
http://www.tigerdirect.com/applications/SearchTools/item-details.asp?EdpNo=2316882&CatId=7387
This is a little over kill, if there ever was such a thing.
$249.99
Power Supply:
http://www.tigerdirect.com/applications/SearchTools/item-details.asp?EdpNo=899123&Sku=T925-5002
Honestly take your pick, Ultra, Thermaltake, Cooler Master, all make good cheep PSUs.
$49.99
Total comming to $563.95. If its too rich for you blood get a 6850 video card, or a different brand 7850 (I made it a MSI to match the motherboard, but you can pick whoever you want) Sapphire is typically a very good lower priced brand. This well fits your price point, even to the point you can get your new monitor right now
. Or better yet add a Solid State Drive from Patriot or OCZ, they are fast, cheep, and more reliable that people lead on to believe.
Im willing to bet that this set up will run anything you throw at it, full steam ahead.