FlexChart is a charting engine written in Flex that uses an XML descriptor to render charts dynamically at runtime. It's designed to be used from Ajax applications where the descriptor is supplied to the SWF dynamically, either generated client side or retrieved from the server. Read the manifesto. There is also a demo page, as well as a binary version and FlexBuilder source from Subversion.
Version 2.0 was released on Oct 20, 2008.
I've blogged about FlexChart a significant number of times. Here's a link to all the posts that mention FlexChart.