Stalk3rchief said:
Hate to ruin the stream of creative answers, but, why not just shoot them? Armor isn't bullet proof or even bullet resistant. Hell, arrows went through the suits.
Maybe a nice fixed gun, like a mounted 50.cal or an M60, with a rather large barrel to finish them all off.
full plate, that is to say gothic plate, was arrow proof, and also largely immune to slashing weapons. the efficiency of bullets however, depends on the period. For example, a pistol shot from the 1600s was stopped more often than not by armour, (as seen on deadliest warrior) but a modern pistol will easily penetrate the plate. likewise, rifles from practically all ages will penetrate plate.
However, this is probably unhelpful and needlessly precise, so my weapon of choice would be the Ray sphere from infamous. steel plate conducts electricity just as well as any other metal. Failing that, Yahtzee's gun that shoots shriuken and lightning (or was it bees?)