The following is a list (by no means comprehensive, and still in progress) of Hispanic Collections available on the internet. Do take a look, they contain incredible documents and photographs.
The Library of Congress - Hispanic Reading Room - Online Collections
The University of Houston Special Collections - Hispanic Collections - Digital Library
The Latin American Network Information Center - Archives and Resources List
University of Alicante, Spain - Text Encoding Initiative - Miguel de Cervantes Digital Library
University of Florida Digital Collections - Digital Library of the Caribbean - Celebrating Hispanic Heritage
Houston Area Digital Archives - Contains oral histories and other resources and documents pertaining to Hispanic History in Houston
The Latino-Hispanic American Experience: The Arte Publico Hispanic Historical Collection Series 1 - EBSCO List