It's official: the benchmarks show that the NVIDIA GeForce 6 Series of GPUs are the GPUs of choice for playing id's Doom 3. Review the benchmarks and link to the full reviews below.
“NVIDIA has told us more than once that the 6800 series was “designed to play DOOM 3,” and the truth of that statement is now glaringly obvious.” --HardOCP
"The Doom III world belongs to NVIDIA. The new NVIDIA GeForce 6800 models proved to offer the best performance for Doom III." --Tom's Hardware Guide

Chart is courtesy of Tom's Hardware Guide. Visit tomshardware.com for the full article.
“The absolute fastest card we've seen for Doom 3 has been the 6800 Ultra series of cards.” --Anandtech.com

Chart is courtesy of Anandtech. Visit anandtech.com for the full article.
“Let’s face it; it’s the GPU in your computer that’ll make the single largest impact on Doom 3’s ability to run good frame-rates for your gaming pleasure… NVIDIA is clearly the better solution for Doom 3.” --Gamers Depot

Chart is courtesy of Gamers Depot. Visit gamers-depot.com for the full article.
NVIDIA's NV40 based cards are without a doubt what you want to be running in your system to get the most out of Doom 3 you can. --Virtual Zone
Visit vr-zone.com for the full article.