Good Doom 3 Tweak Resource

[Insomniak]

I'm puttin this up in software too, but lets face it - it belongs here. This page is a great guide to using your DoomConfig.cfg and autoexec.cfg (you have to create it) files in Doom 3. It goes through how to enable some stuff you might want (such as projectile lights, muzzle flashes, double vision when hit, etc.), and of course lists the settings and what they do and how they affect performance.

Enjoy!

http://ucguides.savagehelp.com/Doom3/FPSVisuals.htm