GhostDoc is a free add-in for Visual Studio that automatically generates XML documentation comments. Either by using existing documentation inherited from base classes or implemented interfaces, or by deducing comments from name and type of e.g. methods, properties or parameters.
It now supports Visual Studio 2005 and also provides experimental support for VB.Net.
If you aren’t using it, give it a try! You’ll love it!
Update: GhostDoc just made it into MSDN-Magazine 12/2005: Visual Studio Add-Ins Every Developer Should Download Now.