There is a tendency to use bar charts and pie charts for all sorts of data. This very often does not communicate well. The chart in a presentation or in a flyer must be chosen based on the message you want to communicate. Here are two useful reference tools if you need help in deciding which graph is best for the message behind your data:
1) Graphics Cheat Sheet (above left) produced by Mike Parkinson (read an interview with Mike on Using Charts in Powerpoint)
2) Chart Chooser from Andrew Abela (above right), also available online: Chart Chooser from Juice Analytics
If you know of any others, feel free to add them in the comments.