Extension for Gnome Shell (GNOME <3.8): gnome-shell-status-only-icon.
This project is discontinued because GNOME 3.8 provide natively the same functionality.
This project is an extension for Gnome shell who display just an icon for status menu.
Also avalaible on:
(Without gnome-shell-status-only-icon)
(With gnome-shell-status-only-icon)