Free VS.NET 2005 like docking including tabbed MDI
All kinds of Third party controls exists to make a tabbed MDI possible.
But (Dutch as I am) was looking for a good looking, free alternative.
I came across DockPanel suite.
Dockpanel suite is much more than a tabbed MDI only .
it's possible to dock panels exactly like in VS.NET 2005. (with the nice looking, user friendly navigation)
Well a picture tells a thousand words:

Weifen Luo has written this open source suite. Version 1.0 is just released which runs on both .NET 1.1 and .NET 2.0.
The source and binaries includes an example application (The screenshot above is taken from the example app)
An extensive cookbook is available for download too (VB.NET version) in a seperate download.
check it out here