Sybian
A Sybian is a device used mostly by women for autoerotic purposes and sexual arousal. It consists of a saddle-like seat containing an electric motor connected to a rod that protrudes from a hole in the centre. Various phallic objects, like dildos, butt plugs, and nubs can be attached to the rod. The Sybian is designed to vibrate when used, while its attachments rotate. This vibration stimulates the clitoris, while the rotation (in a circular motion) stimulates the G-spot. The intensity of either of these actions can be increased or decreased via a control box attached to the Sybian's base via a cord. The combination of the different stimuli can presumably produce more intense orgasms than the user might otherwise be able to experience via autoerotic or other sexual activity.
The Wikipedia has an extended article on the Sybian
