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.
So I got a nice email from Avatech yesterday saying that I could download the full Avatech Utilities for Revit 2010 for free!
If you are signed up with Avatech, you may have got a similar email.
Otherwise, look into it at:
There is a ‘Lite’ version that anyone will be able to get for free.