I've been wanting to do what Visifire has just done for some time now: create stunningly beautiful, animated chart controls. Not only that, but these are open source and available under a GPL 3.0 license.
Not only are they cool and sort of free (with a very reasonably priced commercial license), but they are very flexible. You can, of course, use them in your Silverlight 2.0 application like any other dll, putting them in your XAML at design time, or loading them programmatically at runtime. But also, you can set the properties through JavaScript. So that means if you have a php site where you want to include some chart components, you just load the XAP file into your webpage and use javascript to create the chart. You could either use asynchronous calls to a web service to get your data for the chart, or have your php code generate a data island on the web page that your javascript can then load into the chart. Pretty ingenious if you ask me.
They also have a cool Chart Designer tool on their site that allows you to see the effects of changing the various properties in real time. This saves you from having to do the old "change property > compile > run > determine effect > stop > change property > compile > run > determine effect > stop >" dance.
I'm a little jealous that I wasn't able to create these controls before Visifire, but as much time as I did spend on a similar project, I just didn't have enough time with all the "real work" I've been doing for my clients. So I thank Visifire, and plan to use their charts in dashboards and reporting tools I'll be creating for other clients (gladly paying the appropriate licensing fee when applicable).
Here is my first Test Chart App. Click on one of the columns and a new chart with that column's data further broken down appears. I added an event handler to the DataPoint's click event to initiate the creation of the second chart. I also added some animation which moves the new chart over to the right and fades it in.