My favourite is at the moment (to the tune of voodoo child):
"Magic, Magic, Magic,
You are my voodoo cat, my voodoo cat.
Don't say maybe, Magic
You are my voodoo cat, my voodoo cat."
And to the tune of "Big spender"
"Whenever you walk... in the joint... I know that you're a FAT KITTY"
And I also like to sing the Kaiser Cheifs "Everyday I love you less and less" (without changing the lyrics, but inevitably in a voice I would use to a retarded toddler).
for some reason people think it's acceptable to talk like a retard and sing out of tune to a pet. I. am. a. fan.