Here is a set of JAVA simulations and animations that help you visualize how thecooperative motion of individual particles can make up a wave.
Transverse Wave Simulation -- simulates a transverse wave.
Longitudinal Wave Simulation -- simulates a longitudinal wave.
Transverse & Longitudinal Wave Animations -- illustrates transverse & longitudinal wave motion.
Here is a JAVA simulation that helps you visualize how the sum of two waves of different frequencies leads to beats.
Wave Beats Simulation -- illustrates beats from wave interference.
Here is a set of animations that help you visualize the Doppler effect.
Doppler Animation -- illustrates the Doppler effect.