I found this recipe in one of my herbal magazines for foot oder (I used to *really* have a bad problem with it), tried it, and found that it works really well. Also gave it to my SIL for her teenage son, and she is happy with the results too.
You take about 3tablespoons of ground sage, add about 1/2teaspoon of ground cloves, mix them together, and put the mix into the shoes. At first, do it daily, after a bit can go down to weekly, then to monthly.
An added advantage, besides it killing off the fungus that causes your feet to stink, it also kills Athlete's Foot fungus. Both of those herbs/spices have very strong anti fungal properties. And it smells nice (to me).