Robin Good: If you are looking for a free and simple alternative to SlideShare you may want to give a look to this new free presentation sharing service which allows you to upload PowerPoint and PDF files without much hussle.
Presentations can be viewed in full screen, shared on social media, tagged and categorized, and made available for download if so desired.
The service looks clean, simple to use, and promising. (I needed one).
Examples of other uploaded presentations: http://slideonline.com/presentation/latest
Free to use.
N.B.: There is hardly any information on the site, "About", and "Learn More" links are not working, so be prudent before uploading your whole library here.
Update: As I have just learned from a timely email (who wrote me as am writing this very Scoop - without knowing it) from Julian working on the development team, the only reason is that the service is just brand new... so, just give them time... and lots of feedback.
Try it out now: http://slideonline.com/
(via by Baiba Svenca)