BENSearchable collection of peer-reviewed educational resources. You can limit your retrieval to the free resources. Browse by subject, resource type or audience level. Contains over 15,000 resources, many of which are free.
Started in 1999 by the AAAS and 11 other societies and collaboratives, is is now the National Science Digital Library (NSDL) Pathway for biological sciences education. Resources have been reviewed by the individual societies for standards of quality and accuracy.