You may not here about this, but I really like the Building Museum. Its probably the most impressive interior in DC, seriously. The museum is dedicated to architecture and engineering and the history of DC...dont mis it.
There are really too many restaunts to mention but if you like Tapas go to JALEO (spanish) on 7th street. Its moderately priced (for DC) and is just a very different dining exerience - one not to be missed.
For a decent meal that wont break the bank in DC, this can be tough, short of fast food which is different than many big cities but there are options. If you like malaysian, try "Malasia"..cheap and GOOD.
Let me know what kind of food you like and maybe I can help you more..