Brush up on the basic science involved in Sound and Hearing at the HyperPhysics site from Georgia State University.
Study Physics! covers the concepts of Frequency, Wavelength, & Amplitude.
The National Institute of Health has a Teacher Toolkit with lesson presentations, videos, and demonstrations about hearing.
Amazing Animal Senses — Some examples of how some animals sense the outside world.
Lessons about Sound Waves from Discovery Education.
It's a Noisy Planet. Protect Their Hearing! — a public health campaign to protect against noise-induced hearing loss.
Dangerous Decibels also offers an educator resource guide with lessons and hands-on activities.
For PreK and Kindergarten teachers, take a look at this lesson plan from Scholastic.
Check out these activities on the Physics of Sound.