The Canon 580EX II flash was the top of the line flash but has been superseded by the Canon 600EX-RT speedlite flash.
Full Auto TTL or Manual
The 580EX II supports TTL mode or full manual mode, depending on your style of shooting.
Off Camera Possibilities
The Canon 580EX II flash supports off-camera flash two ways. You can use the onboard optical triggering system with another Canon 580EX II or Canon ST-E2 transmitter. Be advised the optical triggering system requires one flash "see" the other flash or transmitter. This can lead to missed shots if you are shooting outdoors or there is no line-of-sight connection between the two units. The second way is by using Pocketwizards. Connect one Pocketwizard to the flash using the built-in PC sync port. The other Pocketwizard would attach to the camera's hot-shoe. You can shoot wirelessly over great distances or behind subjects without having to worry about line of sight because they work with radio technology.
A plastic flash stand is included with every rental. You can use this stand to attach the flash to a Light stand or to any 1/4-20 threaded screw. The flash stand also allows for use on a flat surface, like a table.