Here soon, nVidia should have their GeForce 6600 out with *gasp* no need for a massive power supply. List price will be $199. I know that is out of your price range by a bit, but honestly it will probably be the best card for the money for Doom 3.

ATI isn't doing well with Doom 3 for some reason. Though, the tables will be turned with Half Life 2, making it a difficult decision for any gamer. Personally, I'm still a fan of ATI for supporting even the highest end cards in Small Form Factor macine. One slot and low power requirements are mandatory in this space.