University of Colorado
University of Colorado: Physics 2000: Einstein's Legacy: Microwave Ovens
A series of pages describing the theory behind microwave ovens and illustrating the manner in which they cook food. Many interactive sections, highly visible content, and interesting explanations. It's definitely worth a visit!
Physics Central
Physics Central: Physics in the Microwave: Microwave Soap
An experiment involving a bar of soap and a microwave through which students explore how microwaves affect molecules.