John 14:12 Verily, verily, I say unto you, He that believeth on me, the works that I do shall he do also; and greater works than these shall he do; because I go unto my Father.
Skeptics ask when any believer has done a greater miracle than Jesus. As it happens, this is an interpretation of this verse that also catches many of us, in thinking that the "works" referred to are miracles.
But the Greek word here (ergon) is not the usual one for miracles; in refers to toil and everyday sort of work - and without (obviously) snubbing our Lord's earthly ministry, I think it is quite obvious that believers have done things to surpass that on earth.
Take a look at how the word is used elsewhere:
Matt. 5:16 Let your light so shine before men, that they may see your good works, and glorify your Father which is in heaven.
Luke 11:48 Truly ye bear witness that ye allow the deeds of your fathers: for they indeed killed them, and ye build their sepulchres.
The one place where ergon does refer to miracles is John 6:28: "Then said they unto him, What shall we do, that we might work the works of God?" Of course, the context and the "worker" is the only thing that allows us to see miracles implied here. The word itself has no such connotation.