Thought I'd resurrect this old thread; I'm now off in Ibiza, but my time in Barcelona was absolutely wonderful, and here are some shops I frequented and recommend to future visitors; I've added them to the "People's List" of dealers pinned above in Free Discussions forum. (maybe ashlobo could also make Outings pages for them if they don't already exist?)
Vives de la Cortada, No 26 Carrer del Call;
Very nice selection of Spanish (primarily) and world coins; good prices mostly, with some exceptions. Quite professional. Owner speaks only Spanish, but the woman at the minerals counter in the other half of their condominium understands French, and helped translate my requests.
Another shop a little further down the same street; more humble inventory, and less professional (more of a pawn shop ambiance) but some good deals to be had on early Spanish copper if you know where to look. (as in, under €5 each). Spanish, but another customer helped translate for me, this time from English.
+Some street markets in the Gothic Quarter; some are open only on Sundays, but others seem to be present full-time, such as this one I found at the harbour (near the Columbus Monument on the waterfront). Again, great deals to be had (one dealer gave me half price on everything!).