Try
http://www.innsidebarcelona.com if you're looking for an apartment.
met some fun lads from Scotland at one of our community meetings and ended up in the apartment they were renting from innside. it was great. View over the port, barbeque on the terrace, leather sofas. The have a range of places, and at reasonable prices too.
For the real budget traveller try Hostal Kabul on Placa Real. Young crowd always buzzing and very cheap.