His birthday was actually 15 January, 1929, but it is recognized today as a Federal holiday.
Via The Writer's Almanac, his words on the intersection of civil rights and the peace movement still ring true after nearly 50 years:
On April 4th, 1967, King delivered a speech called "Beyond Vietnam," in which he strongly denounced America's involvement in the Vietnam War. He was concerned that the war was recruiting poor and minority soldiers, that it was draining resources from much-needed social programs at home, and that it was an unjust war anyway, targeting the poor people of Vietnam. He said, "A nation that continues year after year to spend more money on military defense than on programs of social uplift is approaching spiritual death."
If that is true, the U.S. is pretty much toast.
The link to Ultarunning is one I've made here before, pretty much annually as I look back: to me, one of the most memorable utterances of Dr. Martin Luther King is something he said when he led a civil rights march in Alabama:
We have the right to walk to Montgomery if our feet can get us there.
Something I like to recall during an Ultra when the wheels begin to feel like they are falling off, hoping my feet can get me there.