Does anyone know of any free (critical point I'm afraid) code coverage tools for Visual Studio 2010 Professional edition. I know there are commercial offerings such as NCover and DotCover, but due to budget considerations these can't be considered. For similar reasons, upgrading to versions of VS that come with code coverage built in also can't be considered.
Looking around I see there appears to be loads of free options for Java developers, but there doesn't appear to be any (VS integrated) options for .NET developers. Please note that I am looking for VS integrated solutions. I know there is a free community version of NCover that runs from the command line, but only the commercial edition is integrated with the VS IDE.
Edit: If no one is really aware of any free tools currently available, could anyone provide pointers to tutorials on how to create VS plug-ins that decorate code in the source window?