I stumbled upon two cool online presentation maker sites and started using it for most of my presentations.
They are Prezi.com(the zooming online presentation) and Animoto.com (lets you create exciting videos from images).
This is really cool web app and helps you to give stunning presentation with excellent map-navigation like user interfaces. Its help you easily convey the big picture of the topic to the audience and so on.
Check out some of the samples available at their website http://prezi.com/showcase/
It can take set of images from your computer and create a Video out of it. The best part of it is the graphical and switching effects that were applied on top of the images while producing the video.
Check out the sample listed on their home page to see the beauty of it. You will love it.
Please post a comment if you know any other cool & stunning presentation making websites.