If you need to perk up your Powerpoint presentations, check out Slideshare , "a place to share & discover presentations and slideshows."
You can even search by tags, e.g. library2.0  and collaboration .
If you think you have a dynamite presentation, you can enter it in the World's Best Presentation Contest  and win a prize. Contest judges are presentation gurus including Guy Kawasaki, who wrote The 10/20/30 Rule of PowerPoint  in his blog.
Here are a few of my Slideshare favorites:
10 Ways to a Killer Blog: Getting noticed in the new word-of-mouth network .
Art of the Start 
iPod Nation: a fresh new look at marketing/advertising 
The Social Web: Wikis, RSS, Blogs, Flickr, and MORE! 
Value Creation in Enterprise 2.0 
Also don't forget that Infopeople has a fantastic archive  of presentation materials from past workshops.