Building my own gaming-computer, need help!

[Glokkpod]

Hello, mmo-champs!
I'm trying to put together a computer that is both cheap and can handle games that demand alot of shit (Bad Company 2 etc)
The parts I'm considering are the following:

Cooler Master Elite 430 Midi Tower Black (case)
Cooler Master GX 550W PSU ATX 12V V2.31, 80 Plus, Standard, 2x 6+2pin PCIe, 6x SATA, 120mm fan (powersupply or w/e it's called in english :<)
AMD Athlon II X4 640 Quad Core, 3.0Ghz, AM3, 2MB, 95W, Boxed (processor)
MSI 870A-G54, Socket-AM3 ATX, AMD870+SB850, DDR3, 2xPCIe(2.0)x16, SATA 6Gb/s, USB 3.0, Military Class (motherboard)
PowerColor Radeon HD 6870 1GB GDDR5 PCI-Express 2.0, 2xDVI, HDMI, 2xmini-DisplayPort, 900MHz (graphixcard)
Kingston ValueR. DDR3 1333MHz 4GB, CL9 Kit w/two matched ValueRAM 2GB DDR3 (DDR)
Western Digital Caviar® Blue 500GB SATA 6Gb/s (SATA 3.0), 16MB, 7200RPM (harddrive)
Windows 7 64bit (OS)

(Hope I didn't forget something!)

So tell me what you think and what can be changed, trying to keep it under 800 euro.
Thank you in advance,
Glokkpod.

[Nellah]

I can't look up part prices right now, but it would probably be better to use an i3-2100 and a P67/H67 based motherboard instead of the AMD based unit if you're looking for performance on a budget.

http://www.anandtech.com/bench/Product/188?vs=289 Scroll down to the bottom, the i3-2100 gets about 50% higher performance than the X4 645 in games.

[iSythe]

I can't look up part prices right now, but it would probably be better to use an i3-2100 and a P67/H67 based motherboard instead of the AMD based unit if you're looking for performance on a budget.

http://www.anandtech.com/bench/Product/188?vs=289 Scroll down to the bottom, the i3-2100 gets about 50% higher performance than the X4 645 in games.

Pretty much this. P67 is if you plan to upgrade and want to OC. H67 if you never plan to upgrade it. If you can afford it, i5 2500K is the best price/performance chip currently.
Everything else seems fine.

[nwo]

No point in getting a high end graphics card and a budget CPU that will bottleneck your card in games. Get an i3 2100 if you want a budget gaming CPU and you will be all set. You can always upgrade to an i5 2500k later on if you want to overclock or want/need more cores. An i3 outperforms nearly all AMD CPUs in gaming performance.