Haiku Deck is a great, free, presentation tool available on the web or as an iOS app. It's easy to use, has a ton of example decks and templates, and a really great help and getting started section.
Haiku Deck helps you simplify your message and use images more effectively, as well as keeping a nice clean, consistent format. This follows best practices for presentations (getting rid of the bullet points and paragraphs of text on slides of old).
The presentation works like a slide deck - click on the left to go back, right to go forward, through each slide.
As you start to type some words, Haiku will look for images that match to help you create your presentation. You can also import your own images. They currently have 19 different themes to choose from. When done, you can email, post or embed your deck and it is viewable on any web-enabled device.
It's really easy and fun to use. Try it out for your next presentation.
More Presentation Tools and Resources
Richard Byrne also has some great posts about using Haiku Deck in the Classroom.