Hmm. A common question. I would look at Intel, they have a good upgrade path, AMD AM2 motherboards may not work with upcoming AM2+ CPUs, time will tell. A good reference would be:
http://forumz.tomshardware.com/hardware...e-Gaming-PCs-Budget-ftopict228067.html
from that guide I like the E4300 OC build
$1000 Budget
E4300 OC Build #2
Aim: Strong gaming performance. Super fast processor.
This Intel build is based upon the E4300 and its ability have a cheap overclock. It is merely an upgraded version of the last build.
Why the E4300 again and not the E6300/E6400/E6600? The E6400 and E6300 hvae become Allendale's, and their OC has been impaired. The E6600 is available if you use the X1950Pro instead of the 8800GTS.
Case: (variable, check Case Selection.)
$45
For build purposes, $45 (Centurion 5) is the assumed price. Price may fluctuate depending on case.
CPU: E4300
http://www.newegg.com/Product/Product.asp?Item=N82E16819115013
$169
Another notorious overclocker. This thing can bring out great speeds.
OR
CPU: Intel Core 2 Duo E6600 Conroe 2.4GHz LGA 775 Processor Model BX80557E6600 - Retail
http://www.newegg.com/Product/Product.aspx?Item=N82E16819115003
$313
One of the best C2D overclockers with a whole 4MB of cache.
Mobo:GIGABYTE GA-965P-DS3 LGA 775 Intel P965 Express ATX Intel Motherboard - Retail
http://www.newegg.com/Product/Product.asp?Item=N82E16813128012
$117.99
Proven overclocker. Great stuff, upgrade path to Quad-Core. The D stands for durable.
RAM: Kingston 1GB 240-Pin DDR2 SDRAM DDR2 667 (PC2 5300) Desktop Memory Model KVR667D2N5/1G (x2)
http://www.newegg.com/Product/Product.aspx?Item=N82E16820134045
$130
Sets the stage for a 3ghz OC with an E4300/E6600.
OR
RAM: Patriot 1GB 240-Pin DDR2 SDRAM DDR2 800 (PC2 6400) Desktop Memory Model PSD21G8002 (x2) - Retail
http://www.newegg.com/Product/Product.asp?item=N82E16820220088
$149.98
Sets the stage for a 3.6ghz+ overclock with E6600. Memory overclocks decently.
GPU: EVGA 320-P2-N811-AR GeForce 8800GTS 320MB is the assumed GPU for this build. The price $269.99 is assumed.
Please see the Graphic Card Suggestions for other suggested cards.
SAPPHIRE 100176L Radeon X1950PRO 256MB 256-bit GDDR3 PCI Express x16 H... Video is the suggested GPU for a E6600 build. The price $144.99 is current.
Please see the Graphic Card Suggestions for other suggested cards.
HD: Western Digital Caviar SE WD1600JS 160GB 7200 RPM SATA 3.0Gb/s Hard Drive - OEM
http://www.newegg.com/Product/Product.aspx?Item=N82E16822144415
$52.99
Reasonable sized HD.
DVD: SAMSUNG Black 18X DVD±R DVD Burner With 12X DVD-RAM Write E-IDE/ATAPI - OEM
http://www.newegg.com/Product/Product.asp?Item=N82E16827151133
$30.99
DVD burner. Generic.
PSU: Antec True Power Trio TP3-550 ATX12V 550W Power Supply with Three 12V Rails 100 - 240 V UL, CUL, FCC, TÜV, CE, C-tick, CCC, CB - Retail
http://www.newegg.com/Product/Product.asp?Item=N82E16817371002
$99.99
Great PSU for the price.
CPU Cooling: Scythe SCNJ-1100P 120mm CPU Cooling Fan - Retail
http://www.newegg.com/Product/Product.asp?Item=N82E16835185038
$39.99
Total: $955.93