I've been following the work of Martin J. Eppler of the Universitiy of St. Gallen in Switzerland as one of the few researchers out there working on visual tools and their efficacy in business and learning environments.
He's set up an excellent website called Visual Literacy with the collaboration of other Swiss universities. They are offering e-learning courses in visual literacy to engineers and business people. They also include great resources in the form of fascinating videos and articles on visual literacy and knowledge visualization.
Last but not least, there's the page of pages with a series of interactive maps with links to websites or, in the case of the very useful Periodic Table of Visualization Methods, pop-up examples of the various types of methods. The "Stairs to Visual Excellence" is well worth a visit, as is the "Visualization Studies" diagram.
Mr. Eppler and his colleagues certainly practice what they preach!
Here's the "Visualization Studies" diagram to whet your appetite, but to see the links you'll have to visit the site.