Ask any dispensationalist whether or not Christ is reigning now and his answer would be a definite "yes"--followed quickly by a "but." "Yes, Jesus is reigning now, but his kingdom won't be fully realized until he begins his millennial reign on the throne of David after the Great Tribulation."
That may sound at first like a reasonable theological argument. After all, we Christians who have experienced salvation, but still find ourselves in a fallen, sinful world, are familiar with the concept of "the now and the not yet." The dispensational view of the kingdom, however, is completely wrong.
One of the many complaints I have against dispensationalism is that it essentially robs Christ of his kingdom. It denies what scripture tells us is a present reality.
I ran across an interesting post at Theology Online, entitled "Dispensationalism's Kingdomless King," that addresses what Peter, Paul, and Jesus himself had to say about the kingdom. Check it out here.
Pay special attention to the quote from Peter's sermon at Pentecost. The Apostle explains to us exactly what David was foretelling in Psalm 110, a passage typically used by the dispensationalist as evidence of a physical millennial reign.