In the spirit of Jennifer Tidwell's excellent Designing Interfaces book, there are a few great catalogs of data visualization emerging online.

Start with the oft-cited Periodic Table of Visualization Methods.

There's another excellent collection at Data Visualization: Modern Approaches.

If you're looking for visualization with a less practical, more web-oriented bent, a colleague recently discovered the FWA: Favourite Web Awards site. It's a huge catalog of websites that use interesting, unique designs and visualizations. That's where we found the Uniqlock "clock", and the giant rickshaw pointer.

At any rate, if you're a student of Tufte like I am, you might find it helpful to review a sample of what visualizations and techniques are possible (or even advisable) before plowing ahead on your next "Rich Internet Application".