Pocket Wizard Flash Trigger

The Pocket Wizards are used to remotely fire flashes from a camera. Basically, you put a transmitter on your camera's hotshoe and then a receiver or now transceiver on your flash and put the flash wherever you want it to go.

Then, you take a picture and the PW remotely fires the flash for you. You can also use it to fire multiple flashes at the same time, from different locations. Really cool stuff.

The price runs from about 130 on up depending on what you get.