Source code for the Silverlight controls? You betcha!
It's a new year here at Microsoft and we've published the source code for the Silverlight runtime and SDK controls that are implemented in managed code. Get the source here.
The control list is extensive:
ButtonBase Button HyperlinkButton CheckBox RadioButton CheckBox ToogleButton RepeatButton RangeBase Slider ScrollBar ProgressBar Calendar DataGrid DatePicker GridSplitter TabControl In addition to the source code for the SDK controls, you also get unit tests. For more details check out this post.
--Cheryl