I just built a PC that I wanted to be small-ish, quiet, powerful enough to play the latest games, and reasonably priced. While one can spend many hundreds more and eek out a bit more performance, the additional gains will be minimal. This setup plays current games, including my favorite Starcraft 2, like a champ and costs under $1370 as of this writing:
Parts List
Samsung XL-2370-1 23-Inch Widescreen LED LCD Monitor $310
Intel Core i3 CPU i3-530 2.93GHz $114
MSI N460GTX Cyclone768D5/OC 768 MB Overclocked Graphics Card $185
Corsair CMPSU-450VX 450-Watt Power Supply $70
SilverStone MicroATX Midsize Tower Case TJ08B $95
OCZ 60 GB Vertex 2 Solid State Drive (SSD) $150
Gigabyte GA-H57M-USB3 Motherboard $120
Lite-On 24X SATA DVD+/-RW Dual Layer Drive $25
Logitech Wireless Performance Mouse MX $80