One of my favorite repositories is the library. Any library whether public, private, state or university is going to provide you with some resource having to do with genealogy. I recommend that when you are researching a person or family that you not only look at the individual/family but also the collateral relatives, the area they lived in, and the historical era. Sometimes researching a locality and a historical era can help you better understand a family's life.
One important resource for those of us living in California is the California Libraries Catalog at http://www.calcat.org/. This site allows you to search for a book, video, article, digital image, etc. from the public and private libraries in the state. You can search by keyword, author, and title. It will provide you with information about what materials located throughout the state meet your search term. You can then use that to go to a local library to find your book/material or ask your reference librarian for an inter-library loan.
The other thing I like about this site is that once you find a book or other material that you like, it provides you with the citation for that material that you can then cut and paste into your genealogy database or word processing program. This feature is a nice way to keep track of sources you have looked at.