Best way to improve your Spanish language skills is by reading books and listening to audio books. This app combines both. See translation in English, if you have problems following along.
Included in the app:
Don Quijote de la Mancha: Full Spanish and English text of the book. Audio of the whole book in Spanish.
Trafalgar by Benito Pérez Galdós: Full Spanish and English text of the book. Audio of the whole book in Spanish.