I recently purchased THIS optical slave from FlashZebra. It is compatible with EX flashes, most others are not. I wanted a way to fire my 2 430EX flashes without having to purchase another Cybersync receiver. I received it very quickly and am happy to say it works perfectly. I use it in the #0128 hotshoe adaptor that is listed in the above link. It's an inexpensive way to fire a 2nd flash.