Best Tapas Bars in Barcelona?

Stay off the places near La Rambla. Usually, you will get recommendations to go look in El Born (which is another quarter in the city centre). There, it's definitely better. However, there are pretty touristy places as well, which are really really good but more expensive.
If you go a little bit further into el Born you will be able to find cheaper places. Very nice ones, too. :-)

We have found Barcelona to have the most expensive tourist located tapas bars is Spain. Is Barcelona your only destination in Spain? As a rule we strive to not eat within tourist zones (due to our perceptions of price and food quality). So we recommend you hop on the excellent subway system to get out of the zone and try tapas bars and non tourist locations.

Go to the Boqueria market and try the tapas bars there.
http://www.boqueria.info/mercat-parades.php?tipoparada=2

Check out Ferran Adria. Their watermelon sangria is amazing! Make reservations just in case! http://www.yelp.com/biz/tickets-bar-barcelona

Also check out Cal Pep, one of the most famous tapas restaurants in Barcelona. Everything is fresh and really really delicious! http://www.calpep.com

If you are looking for more suggestions and a local’s input on the most authentic tapas bars, try a tapas tour by Mekomy – I went on it on my last trip to Barcelona, and it was delightful!
http://www.mekomy.com/experiences/160-local-authentic-tapas-tour

You can use a 'tour' -which is aimed to tourists of course- or else you can make your own route by looking at the 'bible' many Barcelonians use for being in the loop on what's up in the city: www.timeout.cat

The only Tapas place I wasn't disappointed with in Barcelona was El Xampanyet, Carrer de Montcada, 22.

Everywhere else we went in Barcelona was either an upscale bar that also served Tapas or a chain (I was surprised to find that most of the recommended Tapas places in Rick's book are chains). This was the only one we found that seemed local, authentic, and worth recommending.

I think we hit about 90% of the tapas bars in Barcelona from Rick's Guide. Hard to pick favorites as you can not really miss IMO.