My friend Yotam Gingold has just released a charmingly simple iPhone app that amuses me very much. It's called iBooBoo:

Do you have a boo-boo? Do you need someone to kiss it and make you feel better? Let iBooBoo provide you with instant relief!

I defy anyone to download it and not immediately start looking around for ways to use it.

IMO the feature it needs most by far is the ability to record your own sound.

Need I mention the possibilities for in-app purchases?