Prezi is described as The Zooming Presentation Editor and is a cloud-based presentation software/ storytelling tool for exploring and sharing ideas on a virtual canvas and its unique is that it enables users to zoom in and out of their presentation media. Checkout the official Prezi introductory video.
Sparkol allows you to build a presentation by concentrating on the content rather than the format a bit like putting a movie together. If you sign up for a paid sparkol accound you also get free access to videoscribe.tv which lets you build animations in the same cartoon style but obviously not quite to the same level as the amazing RSA Animate videos. Heres the official Sparkol introductory video.