Prezi is a free (you can pay for additional features) presentation tool that is totally web based, quick, and simple to use. You are able not only to use Prezis as slide shows, you can also embed, link and e-mail information. Unlike a slide show like PowerPoint, it does not have to be linear. Prezi will allow you to zoom from space to space throughout your presentation. This approach really lends an openness and excitement to your presentation. I also like how simple (albeit limited) the editing tools are. Simply click, type and animate and you are done. While I was using the free one my only complaint was it felt a little like trial and error, and if you are in a rush, Prezi might be a little bit much to perfect on the fly.
Here is a quick presentation I made in about 5 minutes to help you get the idea