Dima, here are some suggestions:
Bars/cool lounges: Cafe Royale (c/nou de Zurbano 3) and Fonfone (c.Escudellers 24) in Placa Reial
Salsitas/Club 22 (c/nou de la Rambla 22) restaurant that turns into a funky lounge after midnight.
Big Clubs:
La Terrazza and Discotheque in Montjuic (electronic/techno)
Jamboree in Placa Reial (hip hop, reggae, jazz)
La Paloma (c/Tigre 27) Latin -- best on Thursday night
--I'm in Barcelona on June 29th & 30th, Ibiza for the month of July, and then Barcelona again on August 1st, 2nd. If you'd like to meet up just drop me an e-mail/pm.
Here's my pic:
http://www.premile.com/images/volcano3.jpg