I have put a list of links for on my sidebar of Revit MEP content that you may or may not want to down load and use. If nothing else, it's a great place to start reverse engineering some families of your own.
If you have some more, please let me know and I will add them. For now I have;
- Acuity Brands Lighting
- Autodesk Seek
- Loren Cook
- Taco Titus