Neowin.net has recently released the free gmail notifier application for windows 7, this tiny application will sit in windows 7 system tray and keep running in the background checking for new mails in your gmail inbox you had configured with the application, it will notify you for any new messages in your inbox.
This particular version of gmail notifier is developed to work on windows 7 only, you can right click anytime to see the subject of all the mails together.
Not only this will also notify you when it is unable to check for new mails due to lost internet connectivity, or due to wrong password.