I want to build a PC, but I'm new to this? GAMING?

I plan on using an AMD Athlon II X4 645 3.1 GHz CPU, with a ASUS M4A89TD PRO/USB3 AM3 AMD 890FX SATA 6Gb/s USB 3.0 ATX AMD Motherboard. What graphics card, sound card, memory, RAM and all that would be a working combination with that stuff. I plan on using this PC for gaming and I would like to run higher-end games, like Crysis 2, GTA IV, Battlefield Bad Company 2, Modern Warfare 2, and all that good stuff, but I don't know how to search all this stuff up. The things that I THINK are most important are the processors and graphics cards, and I already picked a processor and a compatible mobo. Thanks in advance, and could you guys post the complete setup using my mobo and processors?