Dundas, long time ASP.NET Data Visualization Control provider, created a SharePoint version of their Chart controls that look impressive. Check out some live SharePoint demo pages. There are versions available for both Wss3 and MOSS2007. The resulting pages are really small, because the charts are either Flash movies or pictures that are loaded asynchronously. In the demo below (online at Dundas) you can interact with the charts because they are rendered as a Flash movie.
An evaluation version is available for download, I didn't test it out yet, but they promise that it is a full version that will not time out. A watermark will be displayed on rendered images for the evaluation version. Pricing looks also good at less that 2000 US$ for a single server license (no client access licenses).