Robin, Louie the Fly was my grandpa's favourite ad on TV. This what I remember of it:

I'm Louie da Fly, Louie da Fly
Straight from rubbish tip to you.
Spreadin' disease with the greatest of ease,
Straight from rubbish tip to you.
I'm bad and mean and mighty unclean
Afraid of no one, 'cept the man with the can of Mortein!
Hate that word Mortein...
(then sound effects of fly dying) EEEUUW - ARRGGGGGGHHHH!

One spray and Louie the Fly,
Apple of his old mother's eye was Louie,
Poor dead Louie,
Louie the Fly, a victim of Mortein,
MOOOOOOOR - TEEEEEEIN!