Simple, cheap and effective

The old hippie trick of using good old baking soda as an underarm deodorant is catching on as people get tired of spending hard-earned money on pricy deodorants and anti-perspirants that often contain chemicals such as aluminum chlorohydrate, which can cause allergic reactions or worse. Simply wet a wash cloth (or your fingers) and apply a little baking soda to your underarms; it neutralizes odors and absorbs perspiration all day long.

Source: About.com