Having a pace calculator for me is a necessity. I run gazillion of iterations through it when I'm trying to figure out what pace to run or if I'm trying to hit a certain time what pace do I need.
To use the calculator enter 2 of the 3 variables...it time and distance and click pace to see what your pace should be. I've added this as a page and the bottom of my blog for you to use at any time. (sorry the pace piece on this page doesn't line up right)