If I were visiting Barcelona, I would buy these souvenirs:
- A Barcelona Taxi reproduction in Kit-a-car (also in Passeig Sant Joan, but in the corner with Carrer Rosselló). It is a cheap and nice option. It is also a good present for kids.
- T-shirts in El Traster (a shop in Plaça Sant Agustí Vell and a good excuse to explore Barri de Sant Pere). T-shirts cost 12 €. They also have postcards, bags, knitted figures, and almost anything that's pretty and full of imagination).
- Some piece of art in Galeria Maxó (in Portal Nou 29 also very near Plaça Sant Agustí Vell). Prices start at 22 euros for a small 3-D Barcelona door picture, so don't be afraid to go and see what they have. They are open every day from 11 to 21.30 h, so no excuse.