Although very few people have truly flat feet, many runners do have low arches, which can lead to overpronation and foot pain. If your footprint (tested on wet grass to blacktop) comes almost completely filled in, you have low arches—and need shoes with stability and motion control.
SOLUTION SHOE: The Asics GEL-Fortitude 5 is a shoe made for flat-footers that have a neutral gait. The cushioning system decreases shock in both the rearfoot and forefoot, and two layers of memory foam esnure a customized fit that molds to your heels. ($100, asicsamerica.com)