Is there a way to display unread inbox messages in the sidebar of Gmail?

By default, the little bold number in parenthesis next to your inbox should get higher if a new message comes in -but it's hard to see it change.

If you want to be notified when a new email arrives while you are composing one or reading one, turn on desktop notifications.

• Go to your mail settings (click the little gear on the top right, choose: Mail Settings).
• Make sure you are viewing the General settings.  You should be by default.
• Look down the page for Desktop Notifications.
• Click the radio button for  "New mail notifications on

- Notify me when any new message arrives in my inbox"

Now a little pop up will be displayed as you get new messages. You'll see a little snippet of the message too.