Shyam Pillai, also a PowerPoint MVP, runs OfficeTips. This site offers VBA tutorials and samples, as well as both free and commercial add-ins. The add-ins and tutorials on Shyam's site include:
Save the Trees
and many, many more
Tushar Mehta, an Excel MVP, has a site full of Office tips, tutorials and add-ins. The three PowerPoint add-ins Tushar lists on his site are:
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For details on these tools, go to Tushar's site and click on the PowerPoint link in the left hand column.
AlaDat provides PowerPoint tools. The most popular of their tools are the CD creation tools and PrezGuardPro. In addition, they also sell SlideConverter. For details on AlaDat's tools, go to Steve Hetrick's site or Sonia Coleman's site