obviously there is tons of non-touristy things, the hard part is figuring it out...
For a big and bumping late night club, visit Razzmatazz. It's large and full of locals. Usually entails long lines and cover charge. You can buy cheaper tickets in advance for special shows at FNAC in Plaza Catalunya.
Visiting the Gracia neighborhood above Diagonal for the evening gets you away from tourist traps and into some real chilled out locals bars. If you're not into the bar scene, just stroll these streets or post up in one of the many plazas. Meet the locals, enjoy yourself.
Take a picnic lunch, some wine, and a game or two to either Parc Ciutadella or Parc Guell. There will still be tourists, but lots of locals will be doing the same things as well any day of the week.
A 20 minute train ride north or south out of Barcelona city center will take you to some less crowded, less touristy beaches without the much loved "cerveza cola fanta agua beer" vendors.
These are just a few ideas. All in all, try to steer clear of the touristy areas (La Rambla, Barceloneta etc.) and you will eventually run into some real culture and excitement. Let yourself wander with an open mind, and never refuse any local invites.