This page, from The Provincial Scientist website, provides an excellent and easily understood overview of cold, heat and temperature.
http://theprovincialscientist.com/?p=802
Sponsored by the Jefferson Lab - a world-leading nuclear physics research facility funded by the U.S Dept. of Energy - this Frostbite Theater site provides a large number of videos showing liquid nitrogen experiments.
http://education.jlab.org/frost/
This resource is provided by Zona Land Education in Physics and Mathematics and presents a comprehensive discussion of heat, cold and temperature along with animations of these phenomena.
Click here
This page, presented by the Physics in Plain English website, presents the topic of cold, heat and temperature from the physics perspective of energy.
http://plainenglish.viewshare.net/physics/thermodynamics/temperature.shtml
This site, sponsored by the Atomic Lab of the University of Colorado, also includes a discussion of Bose Einstein Condensation.
http://www.colorado.edu/physics/2000/bec/temperature.html