Students love making lights flash so what could be better than 5 lights flashing. The full wave rectifier really come to life when you use LEDs. My first setting up a like of LEDs that all flash during the same half of the cycle then adding two more that cause the middle one to flash during the other half, students get a good understanding of how the circuit works.

An interesting side note is that there is a time between the flashes when the LEDs are off. This is due to the fact that LED's need a minimum potential difference before they light up.