Aaron,
I don't know of any online sites.
Go to the Spanish Tourism office at 845 N. Michigan ave ste 915. (312) 642-1992
They have great free maps! Sort of a 'walking tour' of many cities, so you will know what historic buildings you are looking at as you tour each city. The map is on the last page of each little booklet so you can tear it off and take it with you. Very handy. I always go there to check for info. Last year they gave me a 2500+ page book of EVERY hotel & hostel in spain. Maybe I bugged them too many times and they just wanted me out of there, I don't know.
Also, I have found that the El Corte Ingles maps that you can find in hotel lobbies when you arrive are very helpful because they have the most street names on them. Some maps only list major streets and I never seem to be on any of them!!