There are seemingly an infinite number of free math resources on the Internet. However, very few provide the comprehensive content that are usually found in textbooks. One of these rare sites is Hippocampus. It is part of the Monterey Institute for Technology and Education and provides free multimedia ebooks for a variety of high school subjects and introductory college level courses. Of particular note are the algebra and calculus ebooks that they have on hippocampus.org. I found their online material to be engaging, and have directed my students to the site for review purposes. They have also added a new “mini-site” just for algebra review.
(Not affiliated with any of these folks – just passing along some good study aids.)