Without breaking the bank too much here are a few suggestions
1. http://www.newegg.com/Product/Product.a ... 6819103539
939 pin San diego Revison E Procesor
You want a reveison e for the fact that it runs cooler and has some new instruction sets like sse3. This also is a good over clocker read the reiveiws on the link
$329
2. http://www.newegg.com/Product/Product.a ... 6813128283
gigabyte 939 athlon 64 board
$133
3. http://www.newegg.com/Product/Product.a ... 6820146890
OCZ Platinum rev 2 the best memory you can get also can push it up to 275 Frequency So that means that if you used the athlon64 3700 and set the memory up to 250... times the multiplier of the CPU which is 11 , that would be 11 X 250 = 2750 megahurtz which is more than an athlonFX 55, and this combo will do the overclocking without a voltage change which means no extra heat for the extra clock speed. $174
4. http://www.newegg.com/Product/Product.a ... 6814102509
ATI X800XL 16 pipe card which requires no extra power to run it, which is one less power cable in you case.
$295
5. http://www.tigerdirect.com/applications ... 39&CatId=0
Case and Power Supply $119 - 60 dollar rebate
These are just a few suggestions that I like, others may have a different opinion.
Andy