I remember reading a comment or post somewhere on the internet where the person said they used those anti-bacterial gels that are usually used for cleaning your hands. And since the gel killed the bacteria they supposedly eliminated the smell from their armpits. I can't say if this actually works, or if it is something that's worth doing, I haven't tried it.

One thing that helps for me as addition to using a deodorant, as someone who sweats a lot is shaving the armpits, or even just trimming them. I assume the hairs keep the sweat there, and bacteria thrives in the moist environment and has more food to breakdown and release the smell. Also, and I may be imagining it, but I feel like deodorant works better when it is sprayed directly on the skin instead through the hairs.