The Encyclopedia of Life aims to increase awareness and understanding of living nature by gathering, generating and sharing knowledge in an open, freely accessible and trusted digital resource.

From the Univ. of Arizona. Covers a broad range of biological disciplines with tutorials and quizzes.

Extensive list of links to quality web sites. Or you can search them as a group. From the US government.

Biology dictionary, tutorials, articles, books, and more. Done by a group of interested nonprofessionals but the contents are generally good. Part of the Scientific American Partner Network.

The Massachusetts Institute of Technology is one of the premier science universities. They make all of their courses available on the web. There are over 3 dozen biology courses listed.

Free lectures and lessons on many Biology topics (and all academic areas). A nonprofit effort to provide free education to all.

Covers biological issues from an agricultural perspective. You can search or browse for topics. Strong on areas such as genetic engineering, insects, and of course plants.

Online books in a wide variety of sciences, including biology, nutrition, agriculture.

Lots of information on marine biology, including animals, environmental issues, biodiversity, etc. From a nonprofit conservation society.