The Internet Archive offers over 12,000,000 freely downloadable books and texts. There is also a collection of 550,000 modern eBooks that may be borrowed by anyone with a free archive.org account.

The PhET Interactive Simulations project at the University of Colorado Boulder creates free interactive math and science simulations. PhET sims are based on extensive education research and engage students through an intuitive, game-like environment where students learn through exploration and discovery.

A range of free, open, online courses from leading UK Universities.

Affordable priced textbooks.

edX is a non-profit, massive open online course (MOOC) provider. The majority of edX courses are entirely free to access and most also offer an optional verified certificate track for a fee that varies per course. Courses may consist of video and text content, discussion forums, and a number of problem and assessment types.

Coursera is an education company that partners with the top universities and organizations in the world to offer courses online for anyone to take, for free.
NUS has signed up to Coursera to offer its own MOOCs.

The three State of California Higher Education Systems are working together to provide you easy access to quality FREE and OPEN eTextbooks that everyone and anyone can use for teaching and learning.

A place to view and share educational material made of small knowledge chunks called modules that can be organized as courses, books, reports, etc. Anyone may view or contribute.

A collection of virtual labs, scenario-based learning activities, and concepts tests which can be incorporated into a variety of teaching approaches as pre-labs, alternatives to textbook homework, and in-class activities for individuals or teams.