Here's another suggestion for central Madrid Bars. Can't get any more central than this one. It's called the Bar La Ideal just off the southeast corner of the Plaza Mayor. It's a tiny place and fills up fast at lunchtime. They specialize on cheap-and-good Bocadillos de Calamares as well as their Patatas Bravas. Yums. This too is a place where, surprisingly enough for its location, you find very few tourists inside - maybe because its long, narrow, and usually crowded. Wait staff is all Spanish and the few small tables line right right side of the aisle.

Yeah, that's me in the red shirt sitting on the left in the right-side photo - eating my DELICIOUS fried squid sandwich. Yum!!! It's good Steve took this picture when he did as no 15 minutes later the place was full.

Saludos, MadridMan