An electronic reference about the Earth, its natural environments, and their interaction with society. The Encyclopedia is a free, fully searchable collection of articles written by scholars, professionals, educators, and experts who collaborate and review each other's work. The articles are written in non-technical language and are useful to students, educators, scholars, professionals, as well as to the general public.
The Knowledge Project is an effort to work with the science academic community to build a reliable, openly accessible library of peer reviewed educational science content for college and high school students. Each article is written by experts in their field and then reviewed and vetted by other experts.
The Best Education Site has a selected list of educational websites and educational links in many disciplines including astronomy.
SciTopics is a free, wiki-like knowledge-sharing service for the scientific community. It offers distilled, authoritative and up-to-date research summaries on a wide range of scientific topics.
Action Bioscience is a non-commercial, educational web site created to promote bioscience literacy that provides articles by scientists, science educators, and science students on issues related to seven bioscience challenges: environment, biodiversity, genomics, biotechnology, evolution, new frontiers in science, and bioscience education (some articles in spanish too).
Internet Encyclopedia of Science
The Encyclopedia is an on-line A-to-Z of science maintained by astronomer/author David Darling and is part of The Worlds of David Darling website. The goal is to provide a comprehensive source of information covering all aspects of contemporary science, mathematics, and technology, including historical data and biographies. It is intended to be of use to the interested layperson, student, and academic alike.
Encyclopedia of Life Sciences (ELS)
Provides comprehensive, up-to-date coverage of the life sciences for undergraduates and graduates, containing over 4,600 specially commissioned, peer-reviewed articles from leading scientists around the world (NOT FREE).
Understanding Science is a fun, accessible, and free resource that accurately communicates what science is and how it really works.
Understanding Evolution is a non-commercial, education website, teaching the science and history of evolutionary biology (Spanish version available).
SpringerImages is a growing collection of scientific images that spans the scientific, technical and medical fields, including high-quality clinical images (NOT FREE).
Science Photo Library is a source of high-quality educational imagery, and image provider for the UK science textbook market with more than 300,000 images and 15,000 video clips covering all curriculum subjects (NOT FREE).
National Academies Press (now all ebooks are free)
The National Academies Press (NAP) publishes more than 200 books a year on a wide range of topics in science, engineering, and health, capturing the most authoritative views on important issues in science and health policy. They offer more than 4,000 titles in PDF format. All of these PDFs can be downloaded for free by the chapter or the entire book.
Google eBooks allow to access all your ebooks wirelessly, no matter where you go. Google eBooks stores your library in the digital cloud, so you can read all of your favorite books using just about any device with an Internet connection.
Google Books is a service of digitals books. The initiative has been hailed for its potential to offer unprecedented access to what may become the largest online corpus of human knowledge.
Wikipedia is a free, web-based, collaborative, multilingual encyclopedia project supported by the non-profit Wikimedia Foundation. Its 16 million articles (over 3.4 million in English) have been written collaboratively by volunteers around the world, and almost all of its articles can be edited by anyone with access to the site.
The Library of Congress is the research library of the United States Congress, de facto national library of the United States, and the oldest federal cultural institution in the United States. Located in three buildings in Washington, D.C., it is the largest library in the world by shelf space and number of books.
Project Gutenberg, abbreviated as PG, is a volunteer effort to digitize and archive cultural works, to "encourage the creation and distribution of eBooks." Founded in 1971 by Michael S. Hart, it is the oldest digital library. Most of the items in its collection are the full texts of public domain books.
The Internet Archive is a non-profit digital library with the stated mission: "universal access to all knowledge." It offers permanent storage and access to collections of digitized materials, including websites, music, moving images, and books.
SpaceMath@NASA introduces students to the use of mathematics in todays scientific discoveries.
The Wolfram Demonstrations Project is an open-code resource that uses dynamic computation to illuminate concepts in science, technology, mathematics, art, finance, and a remarkable range of other fields.
The Khan Academy is a not-for-profit initiative with the mission of providing a world-class education to anyone, anywhere.
An excellent resource on educational materials about ocean sciences.
An open source textbook on physical oceanography by Bob Stewart.
An online textbook on oceanography for high school and college students by Bob Stewart.
This book contains material used for an Environmental Geoscience course for first-year college students interested in majoring in the subject.
A great tutorial on remote sensing (last time I checked was not working).
A mixture of topics from digital photography, software utilities, hints and tips on weather satellite reception, and other science and engineering topics.