Recommended: 8 tips for doing data visualization right.

This slide show includes some examples of really bad (and a few really good) graphics with some explanations of general principles for data display.

AllAnalytics – Beth Schultz – 8 Tips for Doing Data Visualization Right. Available at: http://www.allanalytics.com/author.asp?_mc=sem%5Fotb%5Fedt%5Fallanppcm&section_id=1411&doc_id=261787&image_number=1.