A few days ago, Xbox Spokesperson Steven Moore was on the podcast of Major Nelson, where he said Doom 3 (and perhaps also it's expansion, Ressurection of Evil) has been announced as one of the additional 20-plus, originally 12, games that will be backwards compatible for the Xbox 360. Coming with it is also the popular Lego Star Wars.
While this addition is definitely worth it, Microsoft has continued to stay quiet on any further games that they may have planned to add to the ever growing list of games which can now be transferred from the Xbox to the Xbox 360.