RE: Mexican food in Maryland...
You obviously have not been to the "Little Mexico" section of Prince George's County in Riverdale/Hyattsville/Edmonston. If you want authentic Mexican (as opposed to Tex-Mex), my three favorites in the Little Mexico section of the county are:
El Tapatio - 4309 Kenilworth Ave (Seafood soup & BBQ Goat, my fave)
Taqueria Tres Reyes - 5403 Kenilworth Ave
La Sirenita - 4911 Edmonston Rd
All three are noisy, cheap and delicious. There will be a blaring jukebox playing. Lots of dishes with tripe, tongue and goat - don't expect to find jalapeno poppers or steak fajitas. A rudimentary knowledge of Spanish is helpful, but not essential.
If your taste runs more towards Tex-Mex try the Alamo Restaurant at 5510 Kenilworth Ave. Whichever one you go to, skip the dessert and get some baked goods to go at La Fleur de Puebla bakery at 6300 Kenilworth Ave. They have delicious stuff - very traditional Mexican (i.e., not sickeningly sweet) conchas, cookies, coconut cakes etc. I think they may be open 24-hours a day. Just grab a tray and some tongs when you walk in the door and help yourself. If you are there at lunchtime, they make a great torta on their fresh-baked bolillos.
If you like Pollo a la Brasa, try Pollo Fiesta at 6408 Kenilworth Ave. They also serve other solid Mexican fare.