For exploring, searching out decent roads and eventually getting myself unlost, I use my Michelin yellow series 1:200,000 regional maps.
The numbers I have are 234, 235 and a bit of 240 to cover the last eastern bit to Perpignan and a lot of the Med.
The smaller area - but still 1:200,000 scale - "85" and "86" maps, because they are orientated in landscape format, cover the width better using just two maps, but naturally narrower north to south.
Unfortunately these two series are deemed obsolete and being/have been replaced by the 5** series below, but are still easily available on amazon.co.uk secondhand for not much.
My view on the new one at £999.99 is No Thanks!
I also have a few of the newer orange 5** regional maps but the scale is reduced to 1:275,000 and not as easy to read, and it looks on the few I have that quite a few smaller roads are no longer shown.
Going the other way, the IGN Serie Verte 1:100,000 maps give excellent detail and are slightly more durable having a lightly glazed finish.
Lovely maps to search routes and locations with, plus a nice tactile feel and that bit more hard wearing.
The numbers are, from west > east, 166, 167, 173, 174. Unfortunately they don't go so far into Spain.
As far as I checked via Stanfords, still a current map series. Stop Press: Stanfords have them listed as IGN 100K, and are now yellow.
If you just need an overview, then the recommendations in #2 will suffice.