It looks like the best site for finding textbooks that are Calculus-level and above is the American Institute of Mathematics' Open Textbook Initiative. I found the Strang and Guichard there, though I knew of the Strang already. Boelkins is hoping to make it onto their approved list when his text is more complete. They also have two Linear Algebra texts, which I may look at for the Spring, although I really like the text we're using.
For Calculus, I've found:
- Active Calculus, Matt Boelkins (523 pages, single variable, project-oriented)
- Contemporary Calculus, Dale Hoffman (split into 3 books, most Calc I course will need the first two)
- Calculus, David Guichard (single variable, 318 pages, multi-variable available too)
- Calculus, Benjamin Crowell (single-variable, 205 pages, infinitesimal approach, very readable)
- Calculus, Gilbert Strang (multi-variable, 671 pages, MIT, somewhat poor quality pdf - looks like it went through a copy machine)
And for Pre-Calculus, I've found:
- PreCalculus: An Investigation of Functions, Lippman & Rasmussen (568 pages)
- Precalculus, Stitz & Zeager (1092 pages)
- Trigonometry, Corral (180 pages)
Many of my students have very limited budgets. I'm so happy to be able to find what look like good texts that they'll be able to print for under $15. (For the longer texts, I may suggest printing only the relevant chapters to keep the cost down. I think the 1092 pages would cost around $30.)
Eventually I hope to convince my department to use these, or others like them, as the official texts for the courses. (Then maybe we could require a reading device, which would allow the students to have that paid for through student aid.) Many of my linear algebra students had the text on an ipad or similar device. I think they were able to mark it up. Backpacks are going to get lighter, and wallets are going to suffer less.
For both courses, I'll be adding in activities and problems from Exeter (Glenn Waddell's posts on Exeter's problems are very convincing) and this Rich Problems collection. And here's a fun-looking book a few students might be willing to look at, Street-Fighting Mathematics: The Art of Educated Guessing and Opportunistic Problem Solving, Sanjoy Mahajan. I am now making a flyer to post at my office door.
Here's another long list of free textbooks.
[For anyone local to Berkeley, Copy Grafik has good prices. You can print over 300 pages, and get it bound with plastic and vinyl covers for $12.]