Slideshare is the most popular place to share presentation slides. You can find presentations on a wide variety of topics as well as share your own presentations. Uploading your slides enables people to revisit them after the actual presentation, and allows those that could not attend the opportunity to view your presntation.
Slideshare can have enormous reach. It has a lot of passing traffic, people can embed a Slideshare presentation into their own blog or website, so there is the potential for your slides to reach a significant audience beyond your existing online network.
Prezi is a cloud based presentation software that opens up a new world between whiteboards and slides
25 research things, 2010, 14th thing - Slideshare and Prezi http://25researchthings2010.wordpress.com/tag/slideshare
SlideShare: the YouTube of Power Point http://ezinearcticles.com/?Slideshare----The--YouTube-of-Powerpoint&id=3985621
SlideShare for research http://www.hallicious.com/2010/01slideshare-for-research
Slideshare to enhance research http://blogs.warwick.ac.uk/researchexchange/entry/slideshare_too_to/
To learn a bit more about Prezi, read this blog post by Ned Potter (University of Leeds): “Prezi For The Win? Ten Top Tips To Make a Good One"