Class Designer PowerToys for Visual Studio 2010 is released today! It provides a bunch of enhancements to Visual Studio 2010 Class Designer. Click here to download it now.
It has many cool features like pan/zoom window, floating properties window, fast navigation, etc. You could find the detailed feature list in its help document which is available on the desktop after the Class Designer PowerToys is installed.
Besides the binary, the source code is also available. You could extend the PowerToys easily.
If you are using Visual Studio 2005 or 2008, please use the below links to get the previous releases:
Here is the link to its CodePlex site.