One of my biggest battles is smelly shoes. I love to wear shoes that don't require socks (like barefoot running shoes and canvas slip-ons), but in doing so my shoes tend to smell horrible. Even when I toss them in the washing machine and let them air dry, after wearing them a few times they smell again.
I have finally figured out how to keep my shoes (and thus feet) from smelling by using a homemade shoe spray. This recipe is so incredibly easy. Fill half of your spray bottle of choice (a finer spray is better so your shoes don't get nearly as soaked) with vodka and the other half with water. You can add a few drops of an essential oil of your choice to leave behind a nice scent.
To be honest I was afraid that my feet would smell like a mixture of a stale bar and B.O., but so far it has worked exceptionally well. It doesn't smell at all once it dries, and it has been keeping my shoes fresh longer.