SlideShare = The Flick'r of PowerPoint offers something of interest. It's a slideshow sharing site, like Flick'r or YouTube, where you can upload your PowerPoint, Keynote, or other slides to share with others. Upload the slides, tag them with keywords, and open them up to be viewed (and used) by others.

SlideShare describes itself as a "a cool place to host and share presentations. Upload all your slide decks, and find / download interesting presentations."