It'd be better for us to suggest if you fill out this form.
www.tomshardware.com/forum/288241-31-faqs-build-advice-buyer-guides-troubleshooting
Anyways, here's one :
Processor: Intel Core i5 2500k $219.99
HSF: CoolerMaster Hyper 212+ $27.99
Mobo: Asrock Z68 Extreme3 Gen3 ATX $129.99
RAM: Gskill RipjawsX 2x4GB 1.5V CAS9 1600Mhz $54.99
GPU: EVGA SuperClocked 01G-P3-1567-KR GeForce GTX 560 Ti (Fermi) 1GB 256-bit GDDR5 - $219.99
HDD: Samsung Spinpoint F3 1TB 7200rpm $59.99 DVD: LG DVD R/W $18.99
Case: Antec 300 Illusion $44.99
PSU: Antec NEO ECO 620C 620W Continuous Power - $49.99
Total : $830 after rebates (newegg)
This can maxx out Crysis 2 at 1080p.