For the District of Columbia itself go here
. The linked report includes info on most of the substantial projects in DC proper.
I also posted a thread with major suburban projects many months ago, but as that seems to have been pruned, go here
. That's just for big master plans, TODs and stuff like that. No individual buildings. Unfortunately I don't know of a single place where you can find a lot of info about single buildings in ther 'burbs. There's just too much going on. This thread
, however, gives you info on one prominent skyscraper in Rosslyn.