It seems there are a lot of Spanish books (past the copyright expiry date) too. Not many (as yet) audio books in Spanish

http://www.gutenberg.org/browse/languages/es

Does anyone know if you can read them too on Kindle type machines?

interesting list! now i know who most of the spanish streets are named after. re yr question, i followed one of the links and found that there are different formats available. if you know what system yr reader uses then you should be ok. it does have kindle on the list! not sure how many of the books will be useful unless you speak v good spanish though as they seem to be v old books. still, a bit like a browsing through an old book shop which i always find interesting. thanks for the link