A web-based application produces a reasonable amount of data users need to visualize. I can't be bothered building all the charts and diagrams.
Are there any good SaaS apps for charting? I send them the data via some sort of API, they return a chart in real time.
Have a look at the Google Chart API. If you feel comfortable with the idea of Google collecting all your webapp traffic then I think it's good.
You could use the BIRT system, which consists of a report builder system (dredging data from a database), and an online component. Supports PDF reports, and many different chart types.