Intel or AMD? I'm an Intel kind of guy myself, so I'll make you a build based on intel stuffs:
CPU/Mobo/Ram/Hdd/PSU ($500):
http://www.newegg.com/Product/ComboBundleDetails.aspx?ItemList=Combo.722559
Mid-tower Antec 300 case ($75):
http://www.newegg.com/Product/Product.aspx?Item=N82E16811129042
GTX 460 1GB OC ($160 - 30 rebate):
http://www.newegg.com/Product/Product.aspx?Item=N82E16814133326
Total: $735 before rebate (Price rounded up to estimate tax and shipping costs)
Hits your $800 budget, you get a 8 core i7, 8GB ram, 2TB HDD, GFX card with built in HDMI out (with 3D support! OOOoooOhhHh
