try an intel core i3 2120, H67 motherboard (socket 1155), 2x4GB RAM, AMD 6790 or 6850 (depending on budget), 500gb hard drive, a case (i like antec 300), corsair 500w power supply (or greater)
That should be roughly in your budget range. Crossfire/SLI is when you have 2 or more graphics cards working together. You need a motherboard that supports it (and a more powerfule power supply), but it's nice because you can buy one card now, and one later when they come down in price for a cheap upgrade.
can you list the links? Also i would like maximum discounts or rebates if thats possible. Also, is the nvidia gtx 550 ti better than the amd asus 6850? and if i were to get the 6850, which one would i get? (there is sapphire, gigabyte, asus , etc)