Qwiki is a web-based service which allows you to create a presentation made up by images, videos and your own video-voice over.
In Qwiki you act as the "presenter", and occupy a small video window on the top right corner of each show. From there you can introduce any topic, give any explanation or answer any question you may have been asked.
Each "slide" in the show can also be accompanied by additional images, music and videos that may help the viewer explore the topic in greater depth.
Find out more: http://www.qwiki.com/