It is hard to keep up with all the free add-ins and associated utilities that are available for Revit. Here is a partial list:
–ADDED 6 JULY 2011–
Excitech Revit Toolkit
Maybe someone (WikiHelp, AUGI, Revit Forum, RevitLink) should create and maintain a current list of the free add-ins. Is anyone volunteering?
Here is a similar list from 2009:
Fear and Loathing In a CAD vs. BIM World: Current (?) Revit Tools and Addons