Checker Plus for Gmail
I used to swear by Google’s own Gmail Checker, but that’s changed now that I’ve seen Checker Plus. Longtime Chrome extension author Jason Savard has outdone Google. This extension watches over your Gmail account, displays incoming mail as an unobtrusive pop-up -- with optional “You’ve got mail!” style audio alerts -- and lets you cut straight to a message without opening Gmail. It’ll manage multiple Gmail accounts, and, in short, do everything you want to do quickly with Gmail.
The icon on the Chrome toolbar shows the number of unread messages accumulating in your inbox.
Bonus tip: If clicking on a mail link inside your browser sends you to Outlook, download and run Send from Gmail, from Google.