Anything where there are waves produced. Except sound waves example, here are some others:
Light waves are electromagnetic and do not require a medium to travel through. The velocity of light waves is the same in all inertial frames, however the velocity of sound is not.
Even though the Doppler effect equations for light and sound are completely different, at low speeds they both produce approximately the same result. Hence at low relative velocities between the source and the detector, the same equation can be applied for light as well.
Also, the Doppler effect has a major application in the field of space research and has helped scientists towards a major discovery - that the galaxies were moving away, from which the scientists have realized that the universe is expanding. It has also been found that the distant a galaxy, the faster it is moving away.