a quad core system for that price...here goes
BIOSTAR TFORCE TA790GX A2+ AM2+/AM2 AMD 790GX HDMI ATX AMD Motherboard - Retail ............and....
AMD Phenom 9850 BLACK EDITION 2.5GHz Socket AM2+ 125W Quad-Core Processor Model HD985ZXAGHBOX - Retail
http://www.newegg.com/Product/Product.aspx?Item=N82E168...
http://www.newegg.com/Product/Product.aspx?Item=N82E168...
-$20.00 Combo
$268.99
$248.99 (this is a combo item)
the motherboard comes with the newer SB750 bridge which is great for overclocking black editions through ACC...although it has 8x speeds in crossfire and 16x for one card but I like it more b/c of the sb750 bridge..if crossfire is an option in your mind for the future then by all means get the 790fx with sb750 boards which are more expensive but have 16x-16x crossfireX..... as i said before the 9850Black edition (125 watt) can be overclocked higher with amd ACC thing on the sb750 bridge...
COOLER MASTER RC-690-KKA1-GP Black SECC/ ABS ATX Mid Tower Computer Case Real Power Pro 550W Power Supply - Retail
http://www.newegg.com/Product/Product.aspx?Item=N82E168...
$99.99
the PSU in that cooler master 690 case is also a quality real power pro 550 watt series psu which is better then cooler master's previous extreme series, plus the case is also great quality wise with a lot of cooling and cable management system.....i have one
ASUS EAH4850 TOP/HTDI/512M Radeon HD 4850 512MB 256-bit GDDR3 PCI Express 2.0 x16 HDCP Ready CrossFire Supported Video Card - Retail
ASUS Gift - World of Warcraft PC Game BLIZZARD - Trial Edition - OEM
http://www.newegg.com/Product/Product.aspx?Item=N82E168...
http://www.newegg.com/Product/Product.aspx?Item=N82E168...
$169.99 - $30 MIR
I like Asus quality and it is pre-overclocked...u can obviously go with the MSI one but its just my recommendation
G.SKILL 4GB (2 x 2GB) 240-Pin DDR2 SDRAM DDR2 800 (PC2 6400) Dual Channel Kit Desktop Memory Model F2-6400CL5D-4GBPQ - Retail
http://www.newegg.com/Product/Product.aspx?Item=N82E168...
$59.99
good memory for that price...check the reviews for it...OR
if u want dd2 1066 then go with this
Kingston HyperX 4GB (2 x 2GB) 240-Pin DDR2 SDRAM DDR2 1066 (PC2 8500)
http://www.newegg.com/Product/Product.aspx?Item=N82E168...
i92.99 -$30 MIR = $62.99 ....so basically similar in price as the ddr2 800 after MIR (check reviews on newegg..some say rebate might be a little hard to get but since it is newegg so I am sure it'll be ok)
Microsoft Windows Vista Home Premium SP1 64-bit English for System Builders 1pk DSP OEI DVD - OEM
http://www.newegg.com/Product/Product.aspx?Item=N82E168...
$99.99
64bit is the way to go with 4gb ram....
Western Digital Caviar SE16 WD6400AAKS 640GB 7200 RPM SATA 3.0Gb/s Hard Drive - OEM
http://www.newegg.com/Product/Product.aspx?Item=N82E168...
$74.99
very fast HD
SAMSUNG 22X DVD±R DVD Burner with LightScribe Black SATA Model SH-S223Q - OEM
http://www.newegg.com/Product/Product.aspx?Item=N82E168...
$26.99
Arctic Silver 5 Thermal Compound - OEM
http://www.newegg.com/Product/Product.aspx?Item=N82E168...
$5.99
ARCTIC COOLING Freezer 64 Pro 92mm CPU Cooler - Retail
http://www.newegg.com/Product/Product.aspx?Item=N82E168...
$26.99
one of the best amd coolers for that price
Subtotal: $813.91-$30(MIR vga)= $783.91 (after MIR)
Or if u go with the faster kingston ram then=
$843.91- $30(MIR VGA) - $30 (MIR Kingston ram)= $786.91 (after MIR)
...i hope i didnt miss any thing
this is the best comp for your budget with quality components...
as u can see the total price is a good 60-65 dollars less then your range of $850 but u have to keep shipping in mind...otherwise u can go with the 9950black instead of 9850 and 790FX instead of 790GX and get it all for $850 IMHO.....let me know if it works for you..good luck and peace be upon all