An unsupported beta of the DOOM 3 1.05 patch has been released by id. It includes improved widescreen support, and a bunch of tweaks/fixes, mostly multiplayer. According to Robert Duffy's .plan the final version of 1.05 will include the SDK(Software Developers Kit), and a future version will include PunkBuster anti-cheat software. He also mentions the DOOM 3 demo is coming soon... who doesn't have DOOM 3 yet?
The beta patch is only 17.3MB, you can grab it from: