Harvard Dept of MCB - Biology Links
Harvard University (U.S.A) Department of Molecular and Cellular Biology, providing comprehensive reference pages to various online sources of information in the biological sciences.
http://www.mcb.harvard.edu/BioLinks.html

Kimball's Biology Pages
Comprehensive selection of references available on the one site, including dictionary and related articles all intending to improve awareness and understanding of Biology online.
http://users.rcn.com/jkimball.ma.ultranet/BiologyPages/W/Welcome.html

Biology, Agriculture and Horticulture
Provides the largest up-to-date online searchable information about biology, agriculture and horticulture on the Internet.
http://trophort.com

Biology Terms Look Up
Free combined look up on comprehensive Biology related dictionaries and glossaries dealing with a vast range of topics: Ecology, Paleontology, Genetics, Climate Change, etc.
http://www.babylon.com/define/18/Biology-Terms.html

Biology.Synced.Org
A reference for all AP biology students. The site offers notes, animations, tests/quizzes to better understand the concepts of biology. The site parallels with the Campbell Reece Biology Textbook.
http://www.biology.synced.org