Car insurance in Spain is pretty much the same as in the UK, you get basic and fully comprehensive insurance and a variety of policies in between. the only main difference is that roadside assistance is included as part of your policay as standard so you don't need to then buy AA or RAC cover.
There are many insurance companies here, but you generally can’t get the real bargains you can pick up on the internet in the UK. The big companies are Mapfre, AXA, Vitalicio and Linea Directa (Direct Line) and there are a variety of brokers too. If you have a normal car, most of the time Direct Line will be the cheapest, they also speak English and you can transfer your no claims bonus from the UK easily. If you have a van, 4X4 etc. it is worth shopping around.
Balumba - Insurance brokers part of the UK Admiral group
Most of the websites have online quoting, so you check out the diferent prices without leaving your desk!