With my trusty new iPhone in hand I decided to peruse the App Store. I found an application by Wooji Juice called Stage Hand.

Stage Hand is a way to have the power of Keynote in your hand.  You can control Keynote, see upcoming slides, view your notes, and even highlight your slides.  This is the equivalent of Presenter View in the palm of your hand!!

Someone needs to create a version that works with PowerPoint.

Right now, you can hack together a solution using remote desktop software such as Mocha VNC for the iPhone.  It is not quite as nice as a custom app though.