"Blessed are the meek, for they will inherit the earth." (Matthew 5:5) (NRSV)
Jesus seems to have drawn upon Psalm 37:11 to fashion the third beatitude. Psalm 37:11 reads: "But the meek shall inherit the land, and delight themselves in abundant prosperity." (NRSV) Jesus substituted "earth" for "land," thus enlarging the scope of the promise. The Greek term used for "meek" is "praeis." The term appears to be an apt translation of the Hebrew term "anaw" (meek).
Psalm 37:11 helps us grasp what Jesus had in mind. In the Psalm, the meek are portrayed as those who are gentle or considerate. The meek are those who submit willingly to God. The Psalm contrasts such folk with "the wicked," those who resist or oppose God. The kind of meekness Jesus has in mind is manifested toward others and God.
Jesus described himself as "meek" (Matthew 11:29). It is also worth noting that Moses is called "meek' (Numbers 12:3). No leader or would-be leader in the larger Graeco-Roman world would have wished to be so described. In the emerging Roman empire, meekness was generally regarded as a weakness, not a virtue. I find it interesting that the greatest figures in our respective traditions share the distinction of being called "meek."
Jesus, of course, spoke the words in a particular context: the Roman occupation. Many thanks, Rami, for pointing this out. N. T. Wright, in addition to the two authors you have already mentioned, helps us think through the political implications of Jesus' teachings. In this case ("meekness"), Jesus calls for a non-violent response to oppression. He will address the matter more than once in the remainder of the Sermon on the Mount, insisting that meekness includes both our attitude and actions with regard to oppressors. Jesus brand of non-violence requires that we give up the option of hating one's enemies in favor of loving (agape) them, even as we turn the other cheek or willingly walk an extra mile.
What about "inherit the earth?" I suppose it is possible Jesus had a "new earth" in mind. Personally, I think the phrase should be read in the larger context of the meek and their willing submission to God's way or God's rule. Such submission requires that we die to possessiveness, in some way give up what hitherto we've believed to be our due. Strangely enough, when we do so, we find we can enjoy the earth, not because we own a piece of it but simply as our common dwelling place, a gift from God. Genuine possession does not involve ownership but instead gratitude, stewardship, and enjoyment.
Like all the beatitudes, the third one calls us to follow Jesus by opting out of the "game of life" as generally understood and buying in to a new way of life.