I just picked up a pair of Yongnuo 560-IV flash units. The flashes have the ability to transmit wirelessly for off camera flash lighting. The device is fully manual and very affordable at $71.00 each. The instruction manual that came with it is poorly translated into English from Chinese, so I did a lot of button mashing and trial and error. I wanted to figure out how to fire the remote flash while disabling the flash in the camera hotshoe and just having that on camera unit transmit the command to fire the remote flash.