I have a good platform I built myself. What do you recommend?
Hard to say anymore. The industry is in a transition as we speak to PCI express and a new MoBo footprint. However, that will take some time to get off the ground.
What I have (and it works very well) is:
Asus P4c-800E Ultra MoBo
4 Gigs 3200 DDR (however 1 gig is enough)
A 3.4EE processor. Any 2.5 and up would do just fine)
Audigy2 Sound Card (There is a good sound chip on the MoBo but the 7.1 is just fantastic on the Audigy)
I have an EVGA Geforce 6800 Ultra, but an Fx5700 or 5950 Ultra will do great. The Radeon X800 series or 9800 is also a kick card. :-)
I am running dual 19" flat screens (but most games only use one screen. A 20-21" CRT would work great and they are not that expensive
As for the rest of the hardware, I have had good luck with Maxtor or WD drives. I used rounded cables just for the airflow and my case is a Lian-Li Pc-82 aluminum. (doesnt way a ton. LOL. There are lots of cases out there now that are aluminum.