#1: Google Voice
Summary: Make calls, send SMS, preview Inbox, and get notified of new Google Voice messages on your computer. This extension is only available for United States numbers.
Summary: Displays the number of unread messages in your Google Mail inbox. You can also click the button to open your inbox.
Summary: Send content to your Chromecast and other devices that support Google Cast. I use this one personally to stream to my TV, but I know teachers out there are using it in their classrooms as well.
#4: Block Sender (for GMail)
Summary: Block annoying emails in Gmail. Say goodbye to unwanted newsletters, individuals, and other uninvited email senders. Note: free version allows a couple blocks, but there is a paid subscription available.