I have been searching for cool data visualization software for some time.  A few months ago, National Geographic published a special edition magazine that focused on energy usage and made use of many very well made charts.  It spurred me to email National Geographic and inquire about how they make their charts.

I received a very nice email back this morning!  The respondent informed me that the author used Adobe Illustrator to make all of their graphs, but she urged me to look into an IBM project called Many Eyes.  Although Illustrator may ultimately be more applicable to a wider data set, this a very neat Java based program and already has many data sets plotted and available to explore.  This is a site very much worth exploring.