Robin Good: SilkSlides is a web-based platform that offers an alternative to Slideshare by providing an ad-free, clean interface, an easy and straightforward way to upload any PPT or PDF file, and a dedicated URL cum discussion space where your readers or colleagues can contribute and comment your work.
Slides can be viewed in full-screen mode and presentations can be downloaded - if allowed - by readers.
Free to use.
More info / Try out immediately: http://silkslides.com/
Via Robin Good