External Sync Mod for Canon Flash

Michael Bass is offering a neat little mod for you Canon 580 EX speedlight owners. He will add a miniphone jack to the flash for $59.95 plus shipping. For that price, you also get fast turnaround and a cable (shown in the photo) to connect the flash to a Pocket Wizard.

This thing works both ways - tied to a receiver to fire the flash, or with the flash on camera and hooked to a transmitter to fire it (to light up a second flash.)

This will, of course, void your warranty. But the electronics of adding an extra jack are very simple, so I would not expect complications form this particular surgery. But be advised.

There's more info here.