Spain has a great cafe culture in general, while Barcelona's scene is second to none. In preparation for our cross-country road trip, we sampled a little bit of what the city had to offer (to keep our energy up, of course). Tapas joints, coffee shops, ham houses - bits and bites here and there. Our favorite places were often tucked away down side streets, unpretentious (or downright eclectic) little joints that served good food and offered fine company.
Instead of giving a specific recommendation (such a cop out, I know), I encourage you to wander the streets, stopping when a place like this catches your eye. Order the strangest thing on the menu, preferably something you've never tried, and have a go at it.