This post might be a little late for Nil already (did you already go to BCN, or is the trip still ahead?), but just thought I'd post something for others interested in visiting Barcelona in the future.
Much has been already posted already, and I agree with most of the places for food and sightseeing (I say most, because there were some I don't know yet

). So I will limit myself to some suggestions which were not posted yet:
Food:
- For tapas, you shouldn't miss going to the
Ciutat Comtal. It's close to Plaça Catalunya...a definite MUST!
- A unique place to visit is the
Boqueria, Barcelona's market hall and, to me, one of the most beautiful ones I've seen. If you're there, go to have lunch at
El Quim. It's woth a visit!
- Two other places for great food are
Els Quatre Gats and
Cal Pep.
Places to visit:
- If you are football fan, you shouldn't miss the Camp Nou and its
FC Barcelona museum.
- If you're in Barcelona on a Sunday, you should go to the Cathedral. In the mornings, the people there will be dancing the
Sardanas, Catalonia's traditional national dance.
- A very nice day trip is to visit the
Codorniu Winery.