Google Mail Checker Plus
Note: This review addresses v1.17 of the software.
Using Gmail and missing the way Outlook notifies you when you've received a new message? Grab Chrome extension Google Mail Checker Plus--it chimes when you receive new messages, lets you view the message subject, and opens a new Gmail message window when you click on a mailto: link.
Note: This program is donationware. It is free to try, but the author accepts and encourages donations towards further development. This link takes you to this file's page at Google Chrome Extensions, where you can automatically install the file into your Chrome browser.