Hearing about Souvlaki Place got me to thinking about "hole in the wall" type places. Tell me about a hole in the wall restaurant that you eat at (and love) that most people in Baltimore have never heard of.
My place is Fiesta Mexicana, 8304 Philadelphia Road in Rosedale Maryland. You can drive right past them and it's easy to miss. It's a husband and wife team (I believe they're both from Mexico) and it's mostly a take out place - they have about 4 or 5 stools, and a small counter if you want to sit down and eat. You talk right to the Chef (Husband or wife) - they can recommend what is good (to your liking) and they'll cook it for you and bring it over when it's done. My neighbor and I go there for lunch - we've been there 3 times and it never cost over $23 total with 2 sodas each - and we're both big boys who like to eat and we leave full.