I always run a reverb pedal last--I figure that it's supposed to mimic the sound of your amp output bouncing around the room/hall/church/auditorium/whatever, so it makes sense that it's the final processing applied to the signal.
Re: the dirt box order, I don't think there's really any rule of thumb--it only makes any difference when you "stack" them, so just run whatever order sounds best to your ear.