My current favorites are Choice Eliminator and Awesome Tables for Google Sites. They have made my productivity increase.
A recent find was Alice Keeler's Group Maker. It automatically creates groups from a spreadsheet. And, what's even better is that you can use it with Google Classroom to make small groups in Classroom - my most wished-for feature!
Check out some tutorials of my favorite scripts in Scripting & Add-Ons Revealed. Go to fennovation.org for more Google goodness!