I have heard of people using baking soda, talcum powder, scented cat litter, and spraying with Febreze fabric refresher or Renuzit odor neutralizer. All of them seem to be satisfactory for eliminating foul moldy odors.
But for ordinary perspiration odor, I think it would be best to simply wet them down with a garden hose and put them in a boot dryer.

I have tried all the powders, sprays, and home remedies you can imagine, with minimal success. Most will clear out the smell, but it is back just as bad the next time I wear the boots.

What kind of socks do you wear? Cotton socks are the worst, they get damp with your sweat and act like a hippie commune for breeding bacteria. One thing I have found that helps is wearing "antimicrobial" socks. Most premium brands of wool or wool/synthetic socks wick moisture away from your feet to keep them dry, which the stinky bacteria hate, and also contain a component (usually a silver derivative) that inhibits bacterial growth. My personal brand is Smartwool, but I am sure many are just as good. These have made a huge difference for me, even on extended backpacking hunts.

My cousin is a Vet.and he uses a secret powder to rid dogs and cats and their carrying cages of skunk smell and it works right well. You can purchase it in your local drug store. Look in the ladies feminine hygiene section and purchase douche powder. It eliminates skunk odor and should take care of foot smell. After that use Oder Eater brand insoles.

Freezing gram positive aerobes will not kill them. The best idea was hit on earlier. To keep them from stinking, put them on a boot dryer at night to dry them out. To rid them of smell they currently have, spray vigoursly with unscented Febreeze. Oder Eater insoles as sarge alluded to is another good idea.

How bout them Mucks, AJ, they are hard to beat. I bought a pair of WoodyMax mucks 6-7 years ago, got tired of them and bought a pair of Wetlands, and my oldest son is still wearing the Woody Maxs.