At first there was the Gmail Notifier extension for Firefox. And there was the GMailCompose extension for Firefox (made defunct by the WebMailCompose extension). The first displayed an email notification message in Firefox. The second allowed you to have all mailto: links you click automatically send you to a page to compose the email in Gmail. There was also GTray.
And then there now is the official Gmail Notifier from Google. Purely for Windows, it appears unobtrusively in your system tray when installed.
New message notifications appear as a transclucent pane in the bottom right of your screen. (The icon does look a little cutesy doesn't it?)
There's not much more you can do with it.
It's nice to have an official tool from Google that does what all those other homegrown tools do. It's also interesting that Google seems to have incorporated the best of all these amazing tools in their app - mail notification and mailto: link manipulation. Thumbs up to the authors of those neat little tools! Google seems to be copying your ideas!