Canon's little RC-6 (and RC-1) will trigger it, but that's IR so only works from the front. I used the RC-1 with both a 7D and 5DII and it's great.
Since the 1D X doesn't have an IR receiver, I recently picked up a hähnel Giga T Pro II, works well and would be compatible with almost any Canon dSLR. Beyond basic triggering, does interval timing, etc.