This is a megasite of links to most of all the information one can find about Puerto Rico. The list includes most study area topics, e.g., Arte y Cultura, Bibliotecas, Biografias y Personajes, Historia. All in Spanish.
This webpage is an online book on the Spanish language with an added perspective of Spanish in Puerto Rico. The reading includes:
Prologo, por Manuel Alvar
I. La lengua
II. La lengua de Puerto Rico
III. El bilinguismo
It is ideally suited as reference material for a graduate student, teachers, and students in a Spanish for Heritage Speakers course.