GUI service manager for OS X?
I'd rather have this a comment, but for some reason I can only post answers.

Have a look at LaunchControl: http://www.soma-zone.com/LaunchControl/. While it does not offer a menu item to start/stop services it provides a list of all available launchd jobs, their current status and a way to start/stop them with the click of a button.

EDIT

LaunchControl now does offer a menu item for controlling selected jobs: