Money and People--not to be crass, but this is what will be needed to see the Great Commission completed.
Yes, there are other things - like "God-sized vision" and "faith that moves mountains" and "willingness to die" and all sorts of such things. But in the end, these things lead down a path that can be measured by two things - money and people.
Around AD 2000, we had about 420,000 missionaries (counting Protestants, Catholics, Independents, Anglicans): of these, about 10,000 worked among the unevangelized. These 10,000 aren't just Westerners. At bare minimum, we need to double this number. To really make a difference and have a chance of seeing closure, we need to add another zero - that is, 100,000 workers (here's a longer explanation as to why).
Around AD 2000, we spent US$250 million a year on missions to the unevangelized world (World Christian Trends, p. 40). Comparatively, we spend $1.1 billion on missions to the evangelized non-Christian world (parts of Africa & Asia), and $13 billion in foreign missions and $163 billion on home missions to the Christianized world (e.g. America, Europe, Latin America).
The average church member gives about $2.75/week to missions. Doubling this is a worthy goal. But $10/month seems minuscule compared to the need. What if missions-aware members of the church made it their goal to give $100 per month toward ministry to the unevangelized world? That's a much bigger goal, and could make a significant difference.
Money and People: this seems blunt and crass, but if we aren't sending, supporting, and sustaining Gospel planters on the field, how will they go? And if they do not go, how will people hear? And if they do not hear... how will they believe?