Mark 9:1-8 (ESV)
And he said to them, "Truly, I say to you, there are some standing here who will not taste death until they see the kingdom of God after it has come with power."
 And after six days Jesus took with him Peter and James and John, and led them up a high mountain by themselves. And he was transfigured before them,  and his clothes became radiant, intensely white, as no one on earth could bleach them.  And there appeared to them Elijah with Moses, and they were talking with Jesus.  And Peter said to Jesus, "Rabbi, it is good that we are here. Let us make three tents, one for you and one for Moses and one for Elijah."  For he did not know what to say, for they were terrified.  And a cloud overshadowed them, and a voice came out of the cloud, "This is my beloved Son; listen to him."  And suddenly, looking around, they no longer saw anyone with them but Jesus only.
It’s easy to divorce this first verse from all that which comes after it, and lose focus. We tend to think if the generation was to see the Kingdom of God after it has come with power, than something is amiss. This is especially true, I imagine, if one is a millenialist who can’t seem to think of God’s kingdom apart from earthly ideas of what God’s Kingdom means. Jesus often speaks of his generation seeing the kingdom of God, he talks about this in regards to the cup in the events surrounding the Lord’s Supper too. But Jesus rarely means anything at all similar to earthly kingdoms when he speaks of the kingdom of God. Here is no exception, unless one thinks the disciples are hold up in a cave, yet undiscovered by Indiana Jones.
The statement that Jesus gives to the disciples here, finds its fulfillment in the Transfiguration. Of course only a few of those standing there get to see it, though none of them taste death until after Christ’s death and resurrection. This is where they see Gods Kingdom come with power, and it leaves them speechless. It is but a peek at things to come. They get a glimpse of heaven. That isn’t all that is going on there. But it is some of what is going on there. They get to see Jesus for who he really is, the king in all his glory.