Haiku Deck is very similar to PowerPoint and Prezi because it allows users to manipulate the themes and layout of slides. The only thing that I didn't like was that the free version only contained five free themes. If you like a certain theme, then you have to purchase it. Most of the themes that I saw were $1.99.
If this seems discouraging, you can still add pictures by using the built in Internet search or taking your own picture on your iPad. When it is time to present, you simply hit a play button and slide your screen! It's a very user-friendly and easy way to make a presentation without spending a ton of money! It would be perfect for your students to create small collaborative projects and create an interactive activity, where they have to briefly research a topic.