(It appears during forum migration this post got deleted from my blog - so re-posting...)
I'm glad to report today (originally posted 5/19/2010) of another Help Authoring Tool (HAT) vendor to add support for the MSHC format used by Visual Studio 2010. Here is a small blurb from Peter Macej of Helixoft:
VSdocman is a VS add-in for commenting and the automatic generation of class documentation from your C# and VB .NET source code. VSdocman parses the Visual Basic and C# projects (including ASP .NET) and automatically creates MSDN-like documentation, IntelliSense and F1 context sensitive help. You can edit your XML comments with WYSIWYG comment editor which allows inserting complex tables, links, pictures, class diagrams and others. Predefined output formats are HTML Help, MS Help Viewer, Help 2, HTML, RTF, Help&Manual and XML. Contact and other information can be found on product page.
Click here for more information about additional HAT solutions that support MSHC.