For $800 here's what i recommend.
Case: Antec Sonata III 500 Black 0.8mm cold rolled steel ATX Mid Tower Computer Case 500W Power Supply - Retail
Link:
http://www.newegg.com/Product/Product.aspx?Item=N82E16811129024
Price: $124.95
Motherboard: GIGABYTE GA-EP45-DS3L LGA 775 Intel P45 ATX Intel Motherboard - Retail
Link:
http://www.newegg.com/Product/Product.aspx?Item=N82E16813128345
Price: $107.99
Processor: Intel Core 2 Quad Q6600 Kentsfield 2.4GHz 2 x 4MB L2 Cache LGA 775 Quad-Core Processor - Retail
Link:
http://www.newegg.com/Product/Product.aspx?Item=N82E16819115017
Price: $199.99
Ram: Crucial Ballistix 2GB (2 x 1GB) 240-Pin DDR2 SDRAM DDR2 800 (PC2 6400) Dual Channel Kit Desktop Memory - Retail
Link:
http://www.newegg.com/Product/Product.aspx?Item=N82E16820146565
Price: $54.99 ($34.99 after $20.00 Mail-In-Rebate)
Graphics Card: SAPPHIRE 100242L Radeon HD 4850 512MB 256-bit GDDR3 PCI Express 2.0 x16 HDCP Ready CrossFire Supported Video Card - Retail
Link:
http://www.newegg.com/Product/Product.aspx?Item=N82E16814102747
Price: $179.99
Hard Drive: Seagate Barracuda 7200.10 ST3250410AS 250GB 7200 RPM 16MB Cache SATA 3.0Gb/s Hard Drive - OEM
Link:
http://www.newegg.com/Product/Product.aspx?Item=N82E16822148262
Price: $59.99
DVD Burner: LG Black 20X DVD+R 8X DVD+RW 12X DVD+R DL 20X DVD-R 6X DVD-RW 12X DVD-RAM 16X DVD-ROM 48X CD-R 32X CD-RW 48X CD-ROM 2MB Cache SATA 20X DVD Burner - OEM
Link:
http://www.newegg.com/Product/Product.aspx?Item=N82E16827136142
Price: $24.99
Total Price (Including Mail-In-Rebates): $732.89
Total Price (Excluding Mail-In-Rebates): $752.89
Hope you like my suggestion.