Originally posted by StreetShooter
You can buy a slave trigger for about $18 (Made in China one, not the Japan one, but works just as well) at CP.
However, your camera must not have a pre-flash. Some digital cameras flash twice - first time to meter the light, and a second time to actually take the picture. If your camera is this type, then you cannot use the slave trigger, because it will fire on the pre-flash.
You can, however, buy a Digislave, which will do the job (but of course it is more expensive). This will allow the flash to fire on the second flash from your camera.