TabScissors and TabGlue - TabScissors splits two tabs to evenly display on the screen and then TabGlue puts them back together. Great for going back and forth entering grades.
AwesomeScreenShot - Great for screen shots. Includes the ability to do a delayed capture or crop just a partial. Plus you can annotate the screensot and save to desktop or google drive.
ShortenMe - Shortens the url address, copies it to your clipboard so you can paste it easily and creates a qr code that you can use.
SpeakIt - Reads whatver is on the webpage, including Google Docs. Great for kids to listen to what they have written and see if it's actually what they thing they wrote.
Clearly - "With one click, Clearly makes blog posts and articles clean and easy to read. Clearly eliminates all distractions from your online reading experience, and even allows you to browse multi-page articles in one, seamless view."