It may be too late for recommendations, but thought I'd mention Bar Lobo just off from Las Ramblas. It was great, and right next to the hotel we stayed at (Hotel 1898) before a cruise in 2012. We also indulged in a great meal at Moments (located inside the Mandarin Oriental Hotel). We ordered the tasting menu. We were grateful we skipped the cheese course only because the portions filled us up long before we got to dessert. Service was outstanding, and a nice touch was the personalized menu we took home as a souvenir.
In my mind, the top sight to see is the Sagrada Familia, much more fascinating than I anticipated. We spent a lot of time exploring the Gothic Quarter, and ate at a small bar there with lots of small plates. Sorry, I don't recall the name.
If you haven't been to Barcelona yet, I hope you enjoy yourself as much as we did. If you have already been... what were your favorite dinner spots & sights?