AMD Athlon 64 3000+
Epox 9NPA+Ultra
crucial value 2GB(1GBx2)
eVGA 7800GT w/ BF2
Antec P180
Creative Audigy 2 Value
Hitachi T7K250 250GB
NEC ND-3540A
The AMD Athlon 64 3000+ is a very good overclocker and that is why I chose it. It gives you the best bang for your buck. The Epox motherboard is also a very good overclocker.
The RAM I chose overclocks well and is a very reasonable price. Also games like BF2 really take advantage with the extra RAM. Future games will too. The eVGA 7800GT may be a little overkill if you do not plan on playing at higher resolutions. However it is a very powerful card, fits in your budget and comes with BF2 for free.
Case is basically all personal preference and you may not like the looks of the Antec, but it is a very nice case.
If you don't need 250GB of space you can get something smaller. You could even get two drives. One 80GB for OS and applications. Then have a larger one for storage. This adds reductancy and even may help performance.
I left out mouse, keyboard, OS, speakers etc. Tell us if you need those or not.