Circadian Rhythm (Wikipedia)
This extensive dictionary definition from the most popular on-line encyclopedia gives those with little knowledge about circadian rhythms an overview of the topic.
Circadian Clocks Web Course · Video
This site offers a series of lectures in the form of a course on circadian clocks (in the Coursera system). The instructors are Dr. Martha Merrow and Prof. Till Roenneberg from Ludwig Maximilians Universität München.
Circadian Rhythms (Kimball's textbook)
This page correponds to the section on circadian rhythms in John W. Kimball's textbook Biology
(6th Edition, Wm. C. Brown).
The Brain, Circadian Rhythms, and Clock Genes
This article by Dr. Michael Hastings includes diagrams and explanations of circadian clock molecules in flies and mammals.
Sleepless at Stanford
This article by Dr. William Dement discusses the need for adequate sleep and its connection with the biological clock.
The Mammalian Biological Clock · Video
This animation on the Howard Hughes Medical Institute's Biointeractive site describes the molecular mechanism of the circadian clock in mammalian cells.
Circadian Rhythms: Organism, Cell, Genes · Video
This 20-minute video is an elegant lecture by Dr. Joseph Takahashi summarizing research on circadian rhythms from organisms to cells and to genes.
Clocks and Rhythms: Interviews · Video
This page contains links to numerous videos of interviews with biological rhythm researchers who attended the 72nd Cold Spring Harbor Symposium on Quantitative Biology in 2007.