Go to http://apps.exchange.autodesk.com/ and click Autodesk Revit on the drop-down list. A number of free add-ins are already available.
Autodesk Exchange has been active for AutoCAD for a while now, but it looks like this will become a somewhat ‘official’ delivery method for add-ins in the future (think Autodesk Seek for add-ins…)
Direct link:
