Bookboon.com contains free eBooks and textbooks that can be downloaded as a pdf, no registration needed.

InTech publishes more than 2,300 open textbooks and 6 journals in a variety of subjects that fall under the heading of science, technology, and medicine.

MIT OpenCourseWare (OCW) is a web-based publication of virtually all MIT course content. OCW is open and available to the world and is a permanent MIT activity.

Hippocampus offers educators a wide variety of multimedia content online, including videos, animations, and simulations. An additional feature offers educators the ability to create "playlists" for their students, which correlate specifically to their particular instruction material.

The AAPT ComPADRE Digital Library is a network of free online resource collections supporting faculty, students, and teachers in Physics and Astronomy Education.

Founded in 2002 by Nobel Laureate Carl Wieman, 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.