This lesson has had quite a few teachers talking lately. It is an experiment to measure the speed of sound.
Students go outside with their laptops to a place where an echo occurs. The student go to a place which is a known distance from the object causing the echo. They use Audacity on the laptops to record a large sharp sound (I used the sound of hitting a tin with a stick). Students can then analyse the results to find the time between the original sound and the echo, to calculate the speed of sound.
Sample results...

Reference: http://home.exetel.com.au/cmckayelearn/der/waves.html#6
Outcomes covered may include: velocity of waves, measuring velocity, experimental design.

Great lesson!