I just wanted to point out the SEER database to anybody who is interested in visualizing data relating to cancer, from 1973 -2006, for 25% of the US population. You have to fax a consent form to have the data released to you, but it includes somewhere around 2.2 gigabytes of data about cancer diagnostics and could be great source data for visualization.
The SEER site is: http://seer.cancer.gov/
Here's a bit more info about the data: http://seer.cancer.gov/manuals/TextData.Readme.txt
It only takes about 2 hours to receive access to the data after sending in the consent form. The terms of the consent form mainly state that you will not use the data to identify any specific individuals. The terms are here:
http://seer.cancer.gov/cgi-bin/seer_track/view_void_pua.pl
Hope somebody finds this useful!