Here are a few of Revit Apps (Addins) that you can't do without.
Coins Auto-Section Box
Allows you to select and element or elements and create a 3D view with a section box surrounding.
GSA Detail Filter
Gives you extra levels of filtering.
Palladio X BIM WindowsLayout
Allows you to tile your windows quickly and save away favourite settings.
Boost your BIM File Version Checker
I use it primarily to stop the upgrade process if I accidentally open a file in a new version.
Mertens 3D Hatch 22
Creates custom Fill patterns. Can be a little tricky to install but worth it.
There are heaps more in the Autodesk Exchange Apps, but this is just a selection of my favorite free Apps.