To continue my 1st post i recommend
www.newegg.com for all parts they have great prices.
But back to ur build to keep ur build under $800 i would save on the case and get a mid size tower like any from the Cooler Master Elite series or something like the Thermaltake V3 or V4 for around $50.
Next i would find a motherboard. im personally a fan of EVGA so im goin to recommend the EVGA P67 for $199 which you can see at ths link
http://www.newegg.com/Product/Product.aspx?Item=N82E168... .
Now on to the CPU the Evga P67uses a Intel LGA 1155 chip set which means that is what ur CPU has to match in order for it to fit. For gaming i would get a newer Cpu its not needed but it will help with speed and graphics so i would say get the Intel i3-2100 for $124 or i3-2100T for $134.
Both theses CPU's come with heatsinks that will work just fine but if ur like me and want something a little better there not hard to find.
Next i would say power supply. now u dont need one really big just one that will get the job done but still have a little room for if u want to ever upgrade so i would say something from 450w to 600w like the Thermaltake TR2 500w for $79 or 600w $54w/rebate on newegg.
Next lets do hard drive nothing fancy but something with good storage. The Western digital Caviar blue 320Gb at 7200rpm will do just fine for around $45
Video card ok so this is where u want to spend a little more money. Chooseing a card is tricky so make sure of some things one that it will work with ur board two it will fit in ur case. im not to good at chooseing video cards but i would say look for one from the companys PNY, EVGA, and ATI these are good brands. you need to look for something with around 512mb or high ram of DDR# or higher...your looking at about $70 to $150.
You will need a CD/DVD drive anything from sony, Asus, LG, and Samsung in my opinion are good brands. Your lookin at about $15 to $25 for a good one.
After all that you'll around $117 left which you need for ram. the evga board uses 1333mhz so will looking look for that. i like corsair so ill recommend the Corsair XMS3 (2x2GB) Gaming ram for $33. that is 2sticks of 2gb ea for a total of 4gb of ram or the Corsair XMS (2x4gb) gaming ram for $88 that is 2 sticks of 4gb ea for a total of 8gb of ram. the more u have the fast ur games will play...
u can put up to 4 sticks on that evga board so u could buy two packs of the XMS3 ram to fill all the slot and still get 8gb of ram.
This should put u right at the $800 mark. this would not include a monitor, mouse, or keyboard. but if u play with the options you could probaly squezze them in. i hope this helped.
If you have any questions please ask i know this is alot of info at once lol