This is a piece of the National Museum of the American Indian.  I believe this is the newest building on the National Mall.  It's right next to the US Botanical Garden on the Capitol Building end (if you click the pic and go to Flickr, it's mapped if you want to know exactly where it is).

It's a pretty neat building.  Hopefully I can run by there on the way home tonight and get some more pictures (I have a tripod today).  Sometime real soon the wife and I are going to have to go and check it out.  It's one of the few national museums we haven't been to yet.