The app store has a lot of Washington DC apps. and there are lots of podcasts too.
But do any DC locals have a favorite to recommend? audio guides/tours? interactive Metro maps?
I found a podcast called Cultural Tourism DC: Audio Journeys that is free and contains three 40 minute walking guides.
Another podcast called Washington Travelcast looks good too. It has 114 different podcasts for many different sites.
The National Portrait Gallery has a whole series of podcasts describing the many works. It's called Face-to-Face, from the Natl Portrait Gallery. Wow!