Google Notifier displays Gmail and Google Calendar notifications.
Some users may not be satisfied with the default new message pop-up window, but Gmail+Growl offers a simple solution to address this issue. By installing this plugin, you can switch from the standard Google Notifier pop-up to Growl notifications instead.
With a variety of customizable options for Growl displays, you can make your notifications look however you'd like. Plus, since Growl notifications are used by other applications as well, you can enjoy a consistent look and feel across your entire system.
Overall, Gmail+Growl is a straightforward, free plugin that can enhance your email experience on Mac OS X.