MockupTiger is a very powerful Prototyping and Wireframing application. It is web based and can be run on your desktop or you can host it on your own domain. Please visit Mockups website for more details
You can build quick dashboard prototypes by hand typing the data values in a simple grid and get any type of chart you desired.
For e.g it comes with basic set of chart types such as
Bar, stacked, group bar, vertical bar, horizontal bar, line chart, area chart, pie chart, donut chart, funnel chart, gauges, meters, speedometers, thermometers, bubble chart.
On top of this you can use any of the web based widget to represent your data. It is the best prototyping tool for dashboards and web applications.