If you live by a Microcenter, you'll easily save a ton on your CPU. I got my i5 2500k for $160 where Amazon/Newegg is asking $220.
http://www.microcenter.com/search/se...a-Micro-Center
They also even knock off another $40 off the motherboard if you buy a 3rd gen i5 or i7 CPU (which is $50-$70 cheaper than Newegg/Amazon) which totals almost $100 saved since they will most likely price match Newegg's prices (they did for my GPU) as long as there aren't mail-in rebates attached to them.
But the catch is you have to live somewhat close to one. I drove 30 minutes and built a $750 rig from all the parts from there. I just reused my PSU, case, HD and inherited a 110gb SSD from a good friend.
Windows 7 OEM - $120
2500k i5 (plan on overclocking later) - $160
Z77 UD3H Gigabyte Motherboard - $140
gtx 660 - $220
Crucial (2 x 8gig)16gig Ram - $55
Hyper Master 212 EVO Heatsink - $30
Some LG OEM Optical Drive - $20
So really, you could substitute that Windows OS for case/PSU + a small hard drive.
Forgot to mention this gets 70-110 FPS in Stormwind on ultra settings @ 1920x1080 resolution.