I really liked this two part sermon by Tim Conway:
From Weeping to Whipping: The Necessity of Passion in Missions
If the title sounds weird let me help you a little, the "weeping to whipping" part refers to Christ weeping for Jerusalem, and then going in to cleanse the temple. I didn't get it at first.
This is the first sermon that I can recall someone pointing out Christ as our supreme example as to what a missionary should be.