The following sites are general technical support sources.
http://office.microsoft.com/home/office.aspx?assetid=FX01085797
Here's the official home of PowerPoint and also one of the best and richest sources of information and extras. You can also get here from the Help menu within PowerPoint (select Help⇨Microsoft Office Online).
This is my favorite PowerPoint site overall. It's information-packed, with many articles by Geetesh Bajaj about PowerPoint usage. Don't miss the PowerPoint Links page here, with links to other PowerPoint resources-that page alone is worth the visit to this Web site.
www.presentations.com/presentations/index.jsp
A very content-rich site, and a great resource for people who create and present presentations frequently. Though it's mostly PowerPoint-focused, there is some general content as well.
A PowerPoint MVP with a lot of freebies to share, both in terms of tutorial information and in free downloads (including lots of templates). A definite must-see!
There are many good articles here about using PowerPoint to its fullest, from Katherine Jacobs, another PowerPoint MVP.
This is the Web site for Echo Swinford, who was the technical editor on this book. Several good articles here, including a tutorial on Bezier curves with lots of illustrations.