Ali and I went to El Rey last night for margaritas and cheap tacos and it did not disappoint. The restaurant itself is made out of old shipping containers and it has a great patio area (assuming it doesn't rain). The service and tacos were solid, as were the chips and guac. I would definitely recommend it for a cheap, casual spot on U street.
All Souls Bar. Loved it. Corner bar that feels kind of like a hole in the wall, even though it isn't really a hole in the wall at all.