Lindy’s near George Washington University is pretty good. They have a little takeout place under their full service restaurant and many locals from the school and hospital were in and out. They have a huge menu of variety burgers (I had the Greek burger) that were good, but they could have been larger. Prices were pretty cheap for D.C.
If you’re in Alexandria, King Street Blues is a fun, and inexpensive place to go. There are many places nearby where you can spend a lot more money and not have as much fun. It has a funky blues atmosphere with a bar downstairs and restaurant upstairs. Really good Southern, down-home food with a twist.