Barcelona: great for bikes (especially if your team has just won the League!) | Photo: Tom Walton
Barcelona, because of its weather, and because considerable efforts have been made to create cycle lanes, is a great city for cyclists.
It's got a decentish bike-hire service (Bicing) for its residents, plenty of places where tourists can hire bikes [info. in Spanish], not too many hills, a great ride along the Carretera de les Aigues for the casual cyclist wanting to get out of the smoke, and a wonderful natural park (Collserola) for the semi-serious mountain-biker.
Just watch out for those kamikaze taxi drivers (etc), that's all!