I suggest some:
- intel pentium i7 processor,
- 32-64gb ssd for system files - not needed, depend on budget
- 500gb-1tb hdd for storing media files,
- graphic card (harder to choose)
- ati radeon 5830/5850/5870/5970/6850/6950/6970/6990 or
- anything better then g-force gts 250 or anything with higher number, also look at price of those cards dont buy too expensive one - this will eat high amount of your budget
- 8 to 16GB RAM at least ddr3, keep it on mind when you will choose motherboard
- at least 650W power suply with at least 88% efficiency, you have to google some tests etc first to find good one
- dont forget on motherboard, choose one which will support processor you choose,
- and 5.1 audio system with sound card supportiing this will increase your experience and feelings from any game, trust me, cards from creative are pretty high quality
- other stuff: lcd monitor, mouse with high dpi, keyboard, try not to buy wireless - its bad for gaming, some coolers, and case, some DVD or Blue-Ray writer will be good too
- if you save some money use them for paying for bills, because this machine will consumpt much of electric energy
I hope I did not forgot anything.