Runners who are severe over-pronators...

What do you wear on your feet that help with your over-pronation/flat arches?

I usually go with shoes.   Ha, ha! I go with a motion control shoe.  Any good running shoe store will be able to help you pick a good shoe.

I wear Brooks Addiction.

Amy, You might also want to look into seeing a podiatrist and getting orthotics to help.  Best of luck to you. Mary