The links given below provide useful information: 

The PowerPoint FAQ

The most comprehensive PowerPoint FAQ site which is looked after by PowerPoint MVP, Steve Rindsberg. The site is a virtual treasure trove for PowerPoint users from newbie to advanced levels. 

Sonia Coleman Tutorials

The first and the last stop when it comes to creating Auto-run Presentation CD. The tutorials ranging from newbie to advanced. A must see. 

PowerPoint E-zine

Online PowerPoint magazine hosted by Geetesh Bajaj. If you are looking for information to various products, tidbits, howto's or just some interesting PowerPoint trivia. Stop by and take a leisurely tour of this elegantly designed site.  

FAQs and tutorials for Powerpoint (German language)

FAQs und Anleitungen für Powerpoint (deutsche Seite). German PPT FAQ site  maintained by Pia Bork (German PowerPoint MVP)

EchosVoice

PowerPoint MVP Echo Swinford's site.

PowerPoint Art and PowerPoint Photos

Original JPEGs for use in on-screen presentations, as well as shoot 'stock photos' for use in PowerPoint. At this time, about 625 JPEGs available for background formatting in PowerPoint, as well as some stock photos.

Awesome - powerpoint backgrounds

Awesome - powerpoint backgrounds make a great companion to Microsoft PowerPoint®. Professionally designed backgrounds and templates compliment any presentation. Order background templates online, download them today. FREE samples available. Do not forget to check out the Text FX tutorial.

TX Text Control

TX Text Control is an ActiveX component that allows developers to add advanced text processing features to their applications with minimum effort.

NXPowerLite

Neuxpower - Software development company based in the UK have recently developed a tool that reduces the file size of Microsoft PowerPoint presentations. It does this by optimizing the graphics and embedded documents within a presentation.

PowerPoint Heaven