Inside the Cell - from the National Institute of General Medical Sciences
Cells Alive - Animations of cell processes, good pictures
Molecular Expressions - Wonderful primer on animal, bacteria, plant cell and virus structures. Digital
videos of cells in motion, microscopy, and mitosis. Part of the Molecular
Expressions website by Florida State University in collaboration with Optical
Microscopy at the National High Magnetic Field Laboratory.
Biology Tutorial - Good, free, online resource for a quick 'refresher' in such topics as
cell basics, respiration, photosynthesis, DNA replication, viruses, etc.