Nathan at the always excellent FlowingData provides a great guide on what tools are available for getting started with data visualization. He categorizes each tool by the purpose of the visualization (e.g. publication, presentation, analysis, etc.), provides their pros and cons, as well as which tools are currently free.
So far I have only used basic excel tools and Many Eyes, but just downloaded Inkscape and, so far, it looks outstanding (and, no, I did not create the image below).