I Need Your Opinions!

I am planning a trip to Washington, D.C. in March and Nashville and Memphis, TN in May. I need help from those who either live there or have been there to suggest places to eat. I'm looking at no more than $10-$15 per dish. I also welcome coffee shops and places to snack. Also, recommendations on places to see in Nashville and Memphis in general is much appreciated. I think we are stopping in Louisville, KY on the way home. I have been to Washington, D.C. once before, and the reason why I'm going back is the group I'm going with is touring The White House. The Nashville/Memphis trip is a graduation gift. I wasn't supposed to find out so early haha