Get yourself an i7 2600K processor.

I have an Asus P8Z68-VPro motherboard, but just about any asus/gigabyte/evga motherboard with the correct socket would work.

You'll want at least 6-8GB of ram.
But ram is relatively cheap, so my recommendation would be 8-12GB depending on the sockets on your board.

A single video card is generally better than two cards in SLI/Crossfire, or two cards on one physical board.
I'm partial to Nvidia cards, but many like ATI cards too; mine is a GTX 570.

I'd get an SSD drive, for your gaming folder.
It doesn't have to be amazing (although if you plan on putting your OS on the SSD, then a better drive is recommended).
I'm using an OCZ Vertex 3, but many prefer an SSD with an Intel Controller.

I'm not sure exact pricing.
But do recommend an i7 based system.