While in Madrid, we lucked out and "discovered" this tiny bar on Espoz y Mina. The very lively owner-barman makes eating tapas there a very enjoyable experience. This photo is of his mother who does most of the cooking, in a broom closet-sized kitchen.
Some of the tapas we enjoyed were gambas a la plancha, boquerones fritos, sepia a la plancha, pimientos de Padrón, calamares fritos, pinchos morunos. (The latter are highly spiced kebabs of pork). The beer is refreshing, vermouth is served on tap, wines are available, and there's lots more. You can't order dinner here, though, but you can make a very satisfactory meal of tapas and raciones.