Mail Checker for Mac

From Scue:

This is a very simple dashboard widget that displays the number of unread messages in your Gmail or Yahoo! mail account.

As you can see it takes the form of a British postage stamp. The stamp will turn red when you have mail waiting - the number will also increase to display the number of unread messages. Clicking on the stamp will open your mail inbox in your default web-browser.

If you have more than one account then just add more copies of the widget to your dashboard. We appreciate that you're going to need to be able to tell the difference between your different mail accounts in this case - not to worry, Mail Checker is currently available in 4 different flavors.