Contains a variety of lessons, quizzes, labs, web quests, and information on science topics. 

A free resource for biology related information run by enthusiasts from all around the world.

Original, entertaining, interactive biology learning activities.

A free science library and personal learning tool brought to you by Nature Publishing Group. Scitable currently concentrates on genetics, the study of evolution, variation, and the rich complexity of living organisms.

Encyclopedic in scope includes names, checklists, automated tools, identification, species abstracts, distributional data, crop information, plant symbols, plant growth data, plant materials information, plant links, references, and other plant information.

This is an ongoing project to collect all the information about all the species of the world. It offers content at a variety of levels, for students and researchers of all ages.