Budget build: $400-$600
Mid build: $600-$800
High build: $800-$1200
For the most part this would include a single GPU solution over any SLI/Xfire setup. If you get around a 19" monitor 1440x900 resolution you really don't need SLI/Xfire, IMHO. My Mid-range build above would have a $70-$125 CPU (plenty for most), $150-$200 GPU, $60-90 PSU (quality one), $50-$75 Case, $35-80 (2gb - 4gb's CAS 4 stuff), $70-$100 Mobo, & $35 DVD Burner. This would put it just under $600 before any shipping/taxes (if you have taxes). Here's the example:
CPU - $70 Easily OC'd later to 2.8-3 gHz on stock cooling!
Intel Pentium E2160 Allendale 1.8GHz 1MB L2 Cache LGA 775 65W Dual-Core Processor - Retail
http://www.newegg.com/Product/Product.aspx?Item=N82E16819116036
Mobo - $97 shipped. Can be found for less, but just using Newegg for example.
GIGABYTE GA-P35-DS3L LGA 775 Intel P35 ATX All Solid Capacitor Intel Motherboard - Retail
http://www.newegg.com/Product/Product.aspx?Item=N82E16813128059
Memory - $29!!! Best CAS 4 DDR2 800mHz!
Crucial Ballistix 2GB (2 x 1GB) 240-Pin DDR2 SDRAM DDR2 800 (PC2 6400) Dual Channel Kit Desktop Memory - Retail
http://www.newegg.com/Product/Product.aspx?Item=N82E16820146565
GPU - $177 - $20 MIR = $157!! Not the cheapest 9600gt, but definately a good GPU!
EVGA 512-P3-N861-AR GeForce 9600GT 512MB 256-bit GDDR3 PCI Express 2.0 x16 HDCP Ready SLI Supported Video Card - Retail
http://www.newegg.com/Product/Product.aspx?Item=N82E16814130334
Case/PSU combo - $120 - $30 MIR = $90!! Not the greatest, but definately no slouch. Has 34A on 12V rails Earthwatts PSU!
Antec Sonata III 500 Black 0.8mm cold rolled steel ATX Mid Tower Computer Case 500W Power Supply - Retail
http://www.newegg.com/Product/Product.aspx?Item=N82E16811129024
DVD Burner - $37 shipped! Retail version, so will have all of the software included!!
LITE-ON Black 20X DVD+R 8X DVD+RW 8X DVD+R DL 20X DVD-R 6X DVD-RW 12X DVD-RAM 16X DVD-ROM 48X CD-R 32X CD-RW 48X CD-ROM 2MB Cache SATA DVD Burner - Retail
http://www.newegg.com/Product/Product.aspx?Item=N82E16827106057
Total for Mid ranged build ~$545.13 - $75 = $470.13!!! Now just add another $100 for a 8800gts and you have a NICE Mid build for $570!!! I'm sure that this build would do as good if not better than the $1k build that TH just did for their budget build!!