A co-worker of mine shared this with me recently.  It was one of the biggest annoyances in Visual Studio 2005 if you ask me!

How to enable IntelliSense in .skin files

IntelliSence everywhere! That's one of the biggest features in new Visual Studio .NET 2005 (VS 2005). But guess what, it doesn't work out of the box in .skin file  - the place you really need it. Those of you who worked with ASP.NET 2.0 themes understand me . Good news - there is a workaround to enable this feature. Do the following:

1. Go to Tools->Options menu.

2. Pick Text Editor -> File Extesion fom a tree at the left part of Options dialog.

3. Type skin in Extesion text box.

4. Select User Control Editor from Editor dropdown.

5. Click Add and then Ok to close dialog and re-open your skin files.

6. Say something corny about Microsoft.

Enjoy!