A couple favorites from a dozen or so trips to Barcelona. Paco Meralgo - only discovered this one last year. Liked it so much I went back twice in same weekend and again on another trip. It's a few blocks off Passeig de Gracia - some tourists, but lots of locals. Really loved the croquetas de pescado y marisco, pa amb tomaquet and the patatas bravissimas.
Also a big fan of both Pla and Re-Pla. Pla is slightly more elegant/sitdown, whereas Re-Pla can be for dinner but also for tapas. Both near Metro Jaume I, though Pla can be tough to find. On a tiny street in Barri Gotic (between Jaume I and Las Ramblas).