I'm a terrible singer but Cooper seems to like "Incy Wincy Spider". I sing this to him while changing his nappy (if he's fussing) or at other times when he's getting cranky. He always smiles.

Or I just say the line "Elmo is soooooooooooo big" which is from a book I read to him every night. I can just say that line now and he'll smile so much - even without seeing the pictures (it's got a pop up Elmo at the end).