Indezine has thousands of PowerPoint templates and PowerPoint backgrounds.
Ppted has an amazing series of designer PowerPoint templates including the Knowledge Series.
Scrapbookpresentations.com has tons of free scrapbook embellishments.
AbsolutePPT has information on PowerPoint to DVD and PowerPoint to movie.
FlashPPT shows how you can insert Flash in PowerPoint and convert PowerPoint to Flash.
MedicinePPT has free Medicine PowerPoint templates.
ChristianPPT has free Christian PowerPoint templates.
PowerPoint Makeover Kit is the site of the book of the same name. HillsOrient has everyday articles and free wallpapers.
Cutting Edge PowerPoint is the site of the book of the same name — see PowerPoint books.