Windows 7 Tip: 
SlideShare is a new service that helps users to upload PowerPoint or Open Office presentationi files and share them online through a You Tube-like interface. In case you are not familiar, it is a place where you can upload and share your powerpoint presentations.
On the home page you will find a number of tags under which the slideshows are divided. I went for humor and fun tags, found some kool stuff there. If you like a presentation you can mark it as favorite or send to your friends. You can also search presentations based on latest, popular, featured, most commented and most favorited.
It s very simple application, you have to upload your slideshow there. After you upload a slideshow, you can view the small version or go fullscreen (which looks really good), clicking through slides one at a time. Looks like a great tool to share presentations.
have you check out PPTshare Online & the PPTshare Desktop?
http://www.pptshare.com
There is another free presentation hosting service called SlideBoom that is superior to Slideshare. SlideBoom supports animations, transtions, audio and has many other exciting features. Here a couple of comparisons between SlideBoom and Slideshare:
http://presentationslides.blogspot.com/
http://www.frederickding.com/posts/2008/07/two-online-powerpoint-hosting-services-2993/