The Document Outline in Visual Studio 2008
Something I never noticed before is the Document Outline window in Visual Studio (2008?). When editing large XAML files this is particularly useful to help navigate the tree of elements.
If you've never noticed it like me, you can make it show up by using the menu's when a XAML file is open: View->Other Windows->Document Outline. Alternatively, the default key command is Ctrl-Alt-T.
This is *not* a Silverlight specific feature. It works with WPF as well (but not ASP.NET pages). Nice....