"More than 1,500 federally supported teaching and learning resources are included from dozens of federal agencies. New sites are added regularly." Keep up with additions by subscribing to the RSS feed.
Includes textbooks, syllabi, course activities, readings, and assessments for high-enrollment college courses. Students pay no more than $30 for textbooks. All materials are shared under a Creative Commons (CC BY) license unless otherwise noted." Also available via Connexions.
"This 1300 page introductory, algebra-based, two-semester college physics book is grounded with real-world examples, illustrations, and explanations to help students grasp key, fundamental physics concepts."