At my startup (https://www.novus.com/) we've built a financial data viz product using Protovis and D3. Once we've gotten over the initial hurdle of needing to support IE (we don't anymore), SVG graphs are the bomb. They print beautifully and offer virtually endless customization options. If you can code it, you can draw it. Expect easy interop with tools such as jQuery (which makes our graphs interactive) and Tipsy. The latter we use to provide tool tips that show underlying numbers that have gone into drawing any particular graph.