Here is a link to a new blog by Tim Grimm. Each post features a new Revit add-in: some free, and some commercial. Check it out:
Revit Add-Ons
I made a bit of a list of free Revit add-ins myself a while ago, but things change very quickly in the Revit development scene. Here is my old post:
Free Revit add-ins, get your free Revit add-ins…
Thanks for the shout out Luke! 🙂