Andy Ihnatko's pick is a presentation app for iOS: PhotoPresenter by Boinx Software. While Apple's Keynote is great for beautiful and formal presentations on mobile devices, it may not be the right choice for a more informal talk.
PhotoPresenter lets you easily display images as topics come up, instead of restricting you to a linear presentation. It gives you a tray of everything that you deem relevant, along with photo albums that are on the device. When a topic comes up, you can quickly find the image that corresponds with it and put it up on the screen.
There are extra features that you can buy within the app, including a highlighter or spotlight, and the ability to have your company's logo on display when no image is being shown.
For more on PhotoPresenter by Boinx, check out MacBreak Weekly episode 386.