We are implementing an application that needs dockable windows, similar to Visual Studio 2005/2008, but with multiple \"docking sites\", unlike VS\'s single one. Does anyone
I've been using the ActiPro library for several months and it's done me well. It does support multiple docking sites. The support is outstanding and you get some other controls (date picker, etc) that are missing from WPF. To me, for $150 it's money well spent. It worked out of the box, no fuss.
We used to use Divelements for WinForm controls but we think Actipro has better support, so we switched for WPF.
Just my two cents.
Here is another one:
http://www.essentialobjects.com/Products/EOWpf/DockView.aspx
This one has a number of built-in skins that you can switch dynamically. It also has many individual controls (such as a "Splitter" control) that you can use independently.