Plain Bagel (free):
Copy/paste Dimension overrides
Redlines - make annotation families drafting-only and hide them when printing
Model cleanup - purge unused line styles and patterns (great for when you accidentally exploded a CAD file), and consolidate duplicate dimensions, text, or filled regions
Change Level - Change the assigned level of an element without moving it in 3D space

Everything Bagel ($99/yr):
Hide N' Seek - select an element that isn't showing up in a view, press the button, find out exactly why. Filter? Workset? Category off? It'll tell you.
Peekaboo - lists all manually hidden elements in a view so you can unhide them, or override their color to track them down
Unmask - finds elements with manual graphic overrides and lets you reset them selectively
PDF Batch Import - Revit's built-in importer does one page at a time. This does the whole document and lays it out to your title block
A Lot of Notes - takes a .docx and creates text notes laid out to your title block and column width. Great for General Notes, which Revit is bad at handling.