- COLLEGE PHYSICS by Paul Peter Urone, Roger Hinrichs, Kim Dirks and Manjula Sharma published by OpenStax College ISBN 1938168003. Creative Commons Attribution 3.0 License.Free, has various formats, pdf epub, interactive resources suggested from PhET. Creative Commons Attribution 3.0 License https://openstaxcollege.org/textbooks/college-physics
- Light and Matter by Benjamin Crowell Free, CC-BY-SA license http://www.lightandmatter.com/lm/. has interactive activities in Python which looks really cool.
if you know of other free ebooks, drop me a google+ and i will add to the list