Google Mail Checker and Send from Gmail
If you have a Gmail account and don’t mind turning Gmail into your default email program, these two extensions are no-brainers. Google Mail Checker puts a small “M” icon on your Chrome address bar that lists how many unopened messages are waiting for you. Tap on the Send from Gmail icon -- an “M” with an arrow -- and Chrome strips out the URL of the current page, sticking it inside a newly formed Gmail message, ready for you to finish and send. Both of these are from Google; there are lots and lots of Gmail extensions for Chrome, but these are the two I go back to all the time.