i-Clickr PowerPoint Remote
Several PowerPoint remotes caught my attention, and I like i-Clickr best. This app controls live presentations, advancing and rewinding slides from the iPhone. Even better, it shows the current slide, preview of the next screen, or talking notes in your hand.
Note: This link takes you to the vendor's site. From there, you can follow the link to the iTunes App Store, where you can download the latest version of the software.