iPad sleep timer function?

Hi, all!
Really enjoying the iPad, especially the games with touch... so much fun!

I'm wondering if I'm missing something, or if the iPad does not have a sleep timer. I listen to audiobooks on the iPod and set the sleep timer for 30 minutes, as I'm usually dreaming by then. I was hoping the iPad would replace my iPod, but not if I can't make it go to sleep by itself.

If there's no built in function, do you know of an app that would power down the iPad when the time was up? I really want to pass my old iPod on to a friend who needs it.

Thanks!