I've posted about it before but Cerveseria Catalana really is a top place to eat. It's a fantastically social place and a great place to go with a few friends, lot's of people chatting, rubbing shoulders, waiting for a table or a perch at the bar.
It's also a great place to eat on your own. The large oak bars provide a great place to sample the multitude of tapas options without feeling lonely. The staff are really helpful with any confusions and of course the food is fantastic. I always eat too much.
In particular the solomillo de ternera (below) are to die for darling.