SonicPics does something I'd been wanting an app to do for a long time: create annotated slideshows with timing you direct. The demo speaks for itself, but I have to say that, after testing, it works as advertised. There could be some UI tweaks, but the act of creating slideshows that move to the next slide as you speak and when you want them to move is as simple as it gets.
First, you select the photos you want in a show, then you flip to each photo in sequence as you record your voice. The timing of each photo is done in sync to the audio, and that part is quite intuitive. Less intuitive are some of the other controls, but perhaps that's just my penchant for attractively-skinned interfaces.
SonicPics has uses beyond simple photo galleries. I could see using this to walk through a UI demo, for example. The app is flexible and can export .m4v files to YouTube or transfer to your Mac using WiFi. You can try the Lite version here, or buy the full version for $2.99.