While I am not sure that upper body strength has anything to do with your ability to run a marathon or 5K, unless you bulk up it certainly can't hurt. I do know that everybody, non runners included, should be doing some sort of resistance exercise on a regular basis.
As a runner, in order for me to stick to a regular strength program it has to be simple, quick, and convenient. My equipment includes dumbbells, tubing, ankle weights, and an exercise ball. About the only piece I would like that I am missing is a pull-up bar.
My exercises include:
bicycle routine (ab work on the floor)
side leg raises
Get into the habit of spending a few minutes doing 2-3 of these on a daily basis, with something different each time.