I was just in Barcelona. I'd recommend;
Paco Merlago (c/ Muntaneer 171) for excellent seafood tapas. Paella looked good there but I didn't try it. It's also open on Sunday which is nice.
Bar Inopia (Tamarit 104) also good for tapas.
Cerveceria Catalana (c/ Malloca 236) Decent tapas, good local atmosphere.
The bars in the Boqueria market are also nice.