Getting odors out of your shoes

How can you get smells out of your shoes?

I have a pair of shoes I wear to my jobs.
I take them off when I get into someones home and work in my socks.
That way I dont track mud and other things from house to house.

the down side of that is what is on peoples floors.....

This ends up in my socks, and then in my shoes.
My work shoes smell and I have only had them for a month.

I have heard before, that if you leave them in the sun.. it kills odor causing bacteria..
hmm.. me thinks that is an old wives tale.. ? Or is it?

I have machine washed them..
they still stink.

Aside from buying a new pair of work shoes every month.. what helps?
Baking soda?
Baby powder?