Please have a look at the following post for a good list of where add-ons using the API are up to at the moment.
http://cad-vs-bim.blogspot.com/2009/06/current-revit-tools-and-addons.html
What Revit Wants
Please have a look at the following post for a good list of where add-ons using the API are up to at the moment.
http://cad-vs-bim.blogspot.com/2009/06/current-revit-tools-and-addons.html