I came across the Slideshare.net website as I was listening to a webinar for ICPSR's data services. It is a huge repository of slides on any topic imaginable! It is user-driven, so you can add to the repository if you want! There is a free account, but there are also paid account options if you want to be able to upload videos and other modes of information sharing. But it is free to upload your own slides.
Here is some information from their "About Us" page:
Some things that you can do on SlideShare