The gtx 280 is being phased out. This gtx 275 is fairly new to the market and it's a killer card. Also with your budget you can tack on another one of those gtx 275's and run them in SLI and still be under your budget. The case used in this build is a full tower, has great cooling/airflow/ventilation and plenty of room to work with...especially for dual vid cards.
http://www.tomshardware.com/reviews/geforce-gtx-275,2266.html <---Review and benchmarks for the gtx 275 vid card
http://www.coolermaster-usa.com/product.php?category_id=18&product_id=2810 <--- more pics and specs of the case used in this build.
http://www.newegg.com/Product/Product.aspx?Item=N82E16811119160 $149.99
COOLER MASTER HAF 932 RC-932-KKN1-GP Black Steel ATX Full Tower Computer Case - Retail
http://www.newegg.com/Product/Product.aspx?Item=N82E16817139006 $119.99 ($99.99 after $20.00 Mail-In Rebate) Free Shipping*
CORSAIR CMPSU-750TX 750W ATX12V / EPS12V SLI Ready CrossFire Ready 80 PLUS Certified Active PFC Compatible with Core i7 Power Supply - Retail
http://www.newegg.com/Product/ComboDealDetails.aspx?ItemList=Combo.193606 Combo Discount: -$25.00 Combo Price: $514.98 $20.00 Mail-In Rebate
GIGABYTE GA-EX58-UD4P LGA 1366 Intel X58 ATX Intel Motherboard - Retail
Intel Core i7 920 Nehalem 2.66GHz LGA 1366 130W Quad-Core Processor Model BX80601920 - Retail
http://www.newegg.com/Product/Product.aspx?Item=N82E16835233029 $39.99 Free Shipping*
XIGMATEK Dark Knight-S1283V 120mm Long Life Bearing CPU Cooler - Retail
http://www.newegg.com/Product/Product.aspx?Item=N82E16835154003 $4.99
Tuniq TX-2 Cooling Thermal Compound - Retail
http://www.newegg.com/Product/Product.aspx?Item=N82E16814130475 $249.99 Free Shipping*
EVGA 896-P3-1170-AR GeForce GTX 275 896MB 448-bit DDR3 PCI Express 2.0 x16 HDCP Ready SLI Supported Video Card - Retail
Free Cryostasis game w/ registration at manufacturer website
http://www.newegg.com/Product/ComboDealDetails.aspx?ItemList=Combo.193834 Combo Discount: -$5.00 Combo Price: $189.98 $20.00 Mail-In Rebate
OCZ Platinum 6GB (3 x 2GB) 240-Pin DDR3 SDRAM DDR3 1600 (PC3 12800) Triple Channel Kit Desktop Memory Model OCZ3P1600LV6GK - Retail
Western Digital Caviar Black WD1001FALS 1TB 7200 RPM SATA 3.0Gb/s 3.5" Internal Hard Drives - OEM
http://www.newegg.com/Product/Product.aspx?Item=N82E16827151171 $24.99 Free Shipping*
SAMSUNG Black 22X DVD+R 8X DVD+RW 16X DVD+R DL 22X DVD-R 6X DVD-RW 12X DVD-RAM 16X DVD-ROM 48X CD-R 32X CD-RW 48X CD-ROM 2MB Cache SATA 22X DVD Burner - OEM
Total: $1,294.90 | $1,234.90 w/mail in rebates
http://technet.microsoft.com/en-us/evalcenter/dd353205.aspx?ITPID=mscomsc <--- Save yourself some money and dl the 64 bit version of Windows 7