I'm a firm believer in giving back to the community - that's one of the reasons I'm quite fond of open sourcing (parts of) the things I write. On this page, you can find an overview of open source projects I'm involved in.
WCF RIA Services Contrib
This project is coordinated by MVP Colin Blair, a true RIA Services expert. I'm a contributor, mainly focussing on extension methods. You can find an overview of what's available at the WCF RIA Services Contrib Codeplex page.
Silverlight Drag and Drop Manager
"Probably the most customizable, feature-rich, free way to enable Drag 'n Drop in your Silverlight applications"
(yup, I made that tagline up myself ;-))
Silverlight Drag Drop Manager allows you to easily implement drag and drop behaviour in your Silverlight projects by providing a DragSource & DropTarget control, which act as a content container and can contain any SL user control. Highly configurable.
This open source control won the first place in the 2009 Silverlight Control Builder Contest, the third place in the Microsoft Silverlight Application/Library builder contest in Belgium, and has actually been advised by Microsoft as a way to easily enable drag and drop in your applications (or at least, that's what someone I met at a Silverlight session I hosted told me ;-)).
Note: currently, this is an inactive project due to the release of drag & drop functionality embedded in SL.