StateMenu is a desktop popup menu that can be used to monitor and control system resources. It also functions as a regular application menu. It should work with any window manager that either sets the _WIN_DESKTOP_BUTTON_PROXY property (like Xfwm4) or allows direct access to root window button events (like Metacity). Under Nautilus/GNOME and Xfce4 it provides an additional desktop menu. Under the Rox Pinboard you can use it to define a different menu for each mouse button.
StateMenu allows quick access to check and/or change the status of daemons, the cpu frequency, your firewall, etc. without taking up any screen real estate. StateMenu is GTK2-based and fully supports icons. It is written in Python (and a little bit of C to interface with Xlib), and it's configuration is defined with an xml file.