I do not agree with the design approach of the majority of free template databases on the web. Many of these sites are built to attract Google traffic and host cluttered templates that seem nothing more than a more colorful extension of Microsoft's standard bullet point opening screen.
Presentationmagazine.com fits somewhere in the middle. Managed by Jonty Pearce, It hosts some standard PowerPoint templates that I would not use in a design, but also has a number of useful articles.
The really useful content of this web site however is its library of free editable PowerPoint maps. You can download them and color states, countries and continents with your own colors. An excellent resource.