First, I have to apologize to everyone at Researchers Anonymous for leaving the MAH link off my first list. Second, I added a few other links that, while not pertaining strictly to Santa Cruz, are important sources of historical materials and people may not have heard of them yet. These include:
* Linkpendium - Genealogy and Family History
* Internet Archive
* Online Archive of California
Other sites I have used, but which I didn't add to the list because of their more general nature, and because they are already well known, include:
* Google Books
* the libraries at UC Berkeley, Stanford and San Jose State
* San Francisco Public Library
* Library of Congress
These are great times for lazy researchers like me. More and more historical material is being made available online. Let me know if you find any other especially good sites.