Chrome only: Notifier extension One Number checks for unread messages in Gmail, Wave, Voice, and Google Reader and displays the unread count right on the Google Chrome toolbar.

Once you've installed the extension, you'll immediately see the button added to the toolbar, where you can see the previews for each service, and access the settings page. You can enable or disable services that you don't use, and customize the colors or how often the extension checks for new unread messages. It's a simple extension, but if you've been looking for an unread message notifier, One Number might be worth a try. One Number is a free download, works wherever Chrome does.