The grimy industrial cities of the UK has Banksy, who is deconstructing our capitalist system. Barcelona has Pez, and his Happy Fish, who is just that: Happy! I can't help but prefer Pez.
Justin Case has many more street art photos on his website barcelonastreetart.net.
Example of art on the roller shutters of a store. On the right shutter a pair of something that looks like the "Happy Fish" by Pez can be seen making up the eyes of the face.
Barcelona, Barcelona 2010, Street Art