The newspaper LasProvincias.es has published a Tabla de sanciones de velocidad / multas y puntos – table of points and monetary fines that speeding offences attract. Just click on the image to see it full size.
The speed limits are in red circles across the top, and the columns underneath are divided into sections depending on the amount by which someone is speeding (e.g. 31-50 or 51-60 etc in a 30km area). The top row carries a fine but no points (sin puntos). The far right column is the amount of any fine (multa) in Euros for a given speed offence (e.g. €100 with no points for doing 31-50 in a 30km area, or 41-60 in a 40km area, and so on).
I hope this is useful as a ready reference for anyone who’s been fined, or anyone who wants to know their rights in advance. I’ve added this to the Driving Laws section of the Links page as well.