SlideShare gives you access to more than 15 million presentations online, and allows you to share your favorites with others.

You can sign in using LinkedIn or Facebook, and then get access to presentations, which you can filter by category. You can also search presentations by keyword. 

Once you've viewed a presentation you can save it, share it, or 'Like' it. You can follow certain companies to get updated on stuff they share.

SlideShare is a great way to find interesting presentations.