To upload your presentation, you must first create a free Slideshare account here. After confirming your account, you are able to start uploading.
What is especially nice about Slideshare is that, like Youtube, it allows you to embed your slideshow in any web page. You also have the ability to make the slideshow private, if you wish. Here is a slideshow by Francisco Grajales III on Social Media, that I embedded into this post as an example of the sharing capabilities of Slideshare.
One caveat: When I originally tested a PowerPoint presentation, it cut off pieces of text near the top and bottom of the slides. So be sure to give your presentation a decent size margin before uploading.