Takahashi Method
Takahashi uses only text in his slides. But not just any text — really big text. Huge text. Characters of impressive proportion which rarely number more than ten, usually fewer. The goal, he says, is to use short words rather than long, complicated words and phrases.
http://presentationzen.blogs.com/presentationzen/2005/09/living_large_ta.html

Really Bad PowerPoint
Seth Godin talks about common PowerPoint mistakes and how to avoid or fix them. The purpose of PowerPoint is to communicate with your audience. Unfortunately, rather than communicating, PowerPoint is used as a teleprompter of instructor notes, as a written record of what was presented, and as slide handouts that attempt to make it easier for your audience to remember everything.
http://www.sethgodin.com/freeprize/reallybad-1.pdf

Top Ten Slide Tips
Garr Reynolds goes into detail on ten of his top PowerPoint slide suggestions, ranging from limiting bullet points & text, to using high-quality graphics, to choosing your fonts well.
http://www.garrreynolds.com/Presentation/slides.html

Beyond Bullet Points
Cliff Atkinson offers is a method of communicating that helps you effectively persuade, inform and educate your audiences. It’s much more than about pretty PowerPoint slides - it’s about finding the clear and compelling structure that cuts through the clutter and guides people to memorable understanding.
http://www.beyondbulletpoints.com/

Brainy Betty
Here, you’ll find both 100% free content as well as premium-quality for-purchase products, courtesy of CrystalGraphics, all designed to make professional-looking websites, PowerPoint presentations and other office documents.
http://www.brainybetty.com/

Microsoft Office PowerPoint Home Page
Includes support and training from Microsoft Office experts on all versions of PowerPoint, including online training, demonstrations, and webcasts. http://office.microsoft.com/en-us/powerpoint/FX100487761033.aspx

We recommend some of these Microsoft offerings:
Up to Speed with PowerPoint 2007
http://office.microsoft.com/training/training.aspx?AssetID=RC100687671033
Create Your First PowerPoint 2007 Presentation
http://office.microsoft.com/training/training.aspx?AssetID=RC101865831033
Get Visual with SmartArt Graphics in PowerPoint 2007
http://office.microsoft.com/training/training.aspx?AssetID=RC101772971033
Create Your First PowerPoint 2003 Presentation
http://office.microsoft.com/training/training.aspx?AssetID=RC011298761033
So That’s How! Great PowerPoint 2003 Features
http://office.microsoft.com/training/training.aspx?AssetID=RC010413011033
Playing Movies in PowerPoint 2003
http://office.microsoft.com/training/training.aspx?AssetID=RC010738341033