Our new Encyclopedia of Slide Layouts provides 100+ examples of different slide layouts that pass the squint test, using the popular Slide Chooser as the organizing framework for the whole book. In addition to providing real life examples of each type of layout, the book also provides four sources for templates for each slide design, to save you the effort of having to create them yourself.
Here are the links to each of the different sources cited in the book.
Powerframeworks.com hosts many of the layouts described in the book, available as free downloads. The site also offers a library of 10,000 pre-designed layouts available for a US$ 169.95 annual subscription.
Charteo offers 25,000 layouts for 1 euro each, or the entire library for an annual subscription of 799 euros.
Duarte Design's Diagrammer has 4,000 layout templates for US$ 0.99 each free.
And the book of course also features Microsoft PowerPoint's SmartArt (which is included in every copy of PowerPoint, and which I had a small role in helping create). If you have an older copy of PowerPoint (back to 2007), you can download the newer layouts for free here.