The Reina Sofia has a lot of different guides from little ones to big exhaustive ones. What is your price range? They also have little inexpensive guides for particular artists (Miro, Dali, Picasso, etc.) and for specific works (like Guernica).
I go really frequently, so I can pick one up for you the next time I go--probably next week. In fact, when I went this past weekend, they were having quite a sale on posters, post cards, and guides.
Incidentally, the new wing of the Reina Sofia has a great bookstore, an impressive library, and a swanky new cafe. You don't have to pay to go to any of these--just enter on the back side of the museum where the new building is.