Circadian tutorial. A good place to start! A brief lesson with links to several useful tutorials.
Clockwork genes. Geared towards high schoolers, includes online animations and video of lectures by Drs. Joe Takahashi and Michael Rosbash, produced by the HHMI.
BIO 4031. Biological Clocks at Washington University by Dr. Erik Herzog.
Mammalian clock. Animation of the molecular basis of the murine circadian clock.
Fly clock. Animation of the molecular basis of the Drosophila circadian clock.