NASA
Nasa: Imagers: The Electromagnetic Spectrum
NASA site provides information on waves, electromagnetic waves and their wavelengths.
My Science Site
Electromagnetic Spectrum: Colour and Waves
This resource provides information on the different wavelengths that make up the electromagnetic spectrum. Also contains information on waves and color.
Johns Hopkins University
The Electromagnetic Spectrum
NASA related site shows the entire Electromagnetic Spectrum. Provides a brief description of the expansive colored spectrum as well as a related link that provides more details.