e-Textbooks for free
e-Textbooks are becoming more popular. The CK-12 site below has them for free. e-textbooks can immerse the student more deeply than a regular textbook can, by adding video, simulations, motion graphics, interactive quizzes, and more. If you'd like to experience a great set of e-textbooks for free – these work in iBooks on Macs and iOS devices – try Edward O. Wilson's Life on Earth series.
Below are a few suggestions of other technologies that could be used as models and simulations to explore complex systems and processes.
CK-12 is committed to providing free access to open-source content (often called Open Education Resources or OER) and technology tools that empower students as well as teachers to enhance and experiment with different learning styles, resources, levels of competence, and circumstances. Here is a link to their vision statement – it's worth skimming through it.
CK-12's collection of resources include PLIX textbooks. These are interactive, and contain many simulations. Explore this a little. How could a technology resource such as this help your classroom?
Article: 106,000 free teacher-created digital textbooks hit the web – eSchoolNews.