Free Textbooks
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Online textbooks for free!  OpenCourseWare Initiative  
What will happen to education when the learners all realize they can get all the education they need for free?
Textbooks to classes, you can get a great education if you are willing to put in the effort for only the cost of the effort. What will high schools look like 10 years from now? If we are smart, not what it looks like today! 
Online Mathematics Textbooks  
Math Reference Project  
Textbooks in Mathematics  
Abstract Algebra: The Basic Graduate Year (Revised 11/02) 

Can someone again tell me why we are buying textbooks? 
flatworldknowledge used to have free books, now they are low cost. Saylor bought the rights and still gives them away. 
In addition, here is a blog posting with 14 free Alg & Trig textbooks. And another blog post with 34 free Calculus textbooks. 
offers free, downloadable books aligned to state standards. Amazing!  Or how about "Calculus in Context", a free calculus textbook that has had good reviews and is funded by the National Science Foundation.  
The AIM is vetting and posting high quality textbooks that are free and or open source. 
Also offers AP prep classes in addtion to college classes. For AP go to "GED and High School" classes. 

Another Free Calculus book with workbook. 