Online Biology Textbook - a textbook from Maricopa Community College. It has some great diagrams.

The Five Kingdoms of Life - a kids website; the organisms move when you run your cursor over them.
 

Daphnia - information and movies of this crustacean.

Healthfinder - A government site where you can type in the name of an organ or disease, or search for health information by letter: everything from acupuncture to zidovudine (AZT).

Nutrition Information: USDA Food Pyramid, Harvard School of Public Health Information, Canada's Food Guide

Digestive System - A complete tour of the human digestive system with details on each organ's structure and function, comparisons with other animals, and practice quizzes for you.

Virtual Pig Dissection - Has photographs, animations, and functions of organs in the fetal pig. It's a great way to prepare yourself for the fetal pig dissection in lab.

National Geographic Heart site (other human body systems are also available here) - A great learning tool with quiz questions.

The Heart: An Online Exploration - An online exhibit about the heart, vessels, and blood from The Franklin Institute Science Museum.

The Heart - A great online lesson from the Texas Heart Institute.

Nervous System - This site, called "Neuroscience for Kids," has great diagrams and simple explanations about the human nervous system, especially the brain and spinal cord.

Neuroscience - From the Society for Neuroscience.

The Eye - Has great diagrams and photos of the eye and explains the functions of its parts.

Life's Greatest Miracle - This PBS online video shows human rproduction and development . It consists of 8 segments, 5-9 minutes each, with scenes from human gametogenesis through birth. You might want to watch all or just some segments.

Developmental Biology - A portion of The Biology Project from the University of Arizona, this site has tutorials, links, and virtual embryos.

Multi-Dimensional Human Embryo Project - An atlas of human embryos, made by magnetic image resonance (MRI), that allows users to view cross-sections or whole embryos from different angles. There are also links to atlases of mouse, chick, and opossum embryos.

Plant Structure - From the Online Biology Book, this is a chapter on plant structures and functions, covering roots, stems, and leaves.

Carnivorous Plants - Information on ecology, cultivation, conservation, and taxonomy of carnivorous plants.