This may also work for other WM like Fluxbox and TWM.
The Debian menu builds a menu from all the installed applications on your system and nicely organises them. I believe it also keeps it updated when you install new software so you do not have to manually add items to your Openbox menu.
To install it use:
sudo aptitude install menu
After it is installed run:
To enable the menu in Gnome go to the desktop panel menu:
System / Preferences / Main Menu and enable the Debian menu under Applications.