If you build SharePoint Developer Tools, you should investigate the Visual Studio Industry Partner Program. There is lots of value in the program for Developer Tools vendors and SharePoint Developer Tools vendors can be part of it.
Also, if you build a SharePoint Developer Tool that can be used with or in conjunction with Visual Studio go ahead and add it to the Visual Studio Gallery.
I have added the Visual Studio 2008 extensions for SharePoint there. Be the first person to write a review of it or rate it.