This is one I wrote with my best m8 KC (also mentioned in my profile :P)
As our powers join together in harmony
With I in you and you in me
Reunited as one with the Power of Three
Fighting together, we will always be
Prue, the oldest who sadly passed away
We call for her to come today
The Power of Three will be no more
From now on, it's the Power of Four
The oldest would lead them in the fight
The youngest would guide them through the night
But Phoebe and Piper, what would they do?
They would help with the magic and cast spells too
Slowing down and speeding up time
The other levitates and thinks up a rhyme
She calls upon the Haliwell poer
In this night and in this hour
Quick! Turn! Look!
There's the demon, straight from the Book
Prue, Piper, Phoebe, Paige
The root of all the demon's rage
Vanquish the demon, save the day
They wouldn't have it any other way
Evil's the pain, it will twist and bend
Haliwell sisters, victorious in the end