When I start teaching Physics, it took me a great effort to explain to students what is transverse wave and what is longitudinal wave, and yet half of them were still stared at me with puzzled eye. When I start teaching by using computer about 5 years ago, it took me only 2 minutes to complete my task and 100% of the students understood what I was talking about.
I just said, "Look, this is transverse wave. The wave travels from left to right whereas the particles vibrating up and down. Transverse wave is a wave where the vibration of the particles are perpendicular to the direction of propagation of the wave.
And then I said, "Look, this is longitudinal wave. The wave travels from left to right and the particles also vibrating left-right. longitudinal wave is a wave where the vibration of the particles are parallel to the direction of propagation of the wave.
And, that's it!
[Notes: The webpages above contain java applet. You need a Java Runtime Environment plug in to play the file. Java Runtime Environment can be downloaded from http://www.java.com/en/download/index.jsp]