Is it just your armpits that smell, or all over? I smell like exercise sweat all over, and there's not much you can do about that. On really long rides I used to come back smelling like ammonia, but it was because I wasn't consuming enough carbohydrates on my rides. The ammonia smell comes from your body breaking down protien (mostly from muscle!) to be used as fuel. I increased the amount of carbs, and stopped smelling like ammonia. Now I just smell sweaty.

For my underarms, I use a combination of a crystal deodorant (available at healthfood stores) and Secret Platinum. The first time I put the Secret on my husband got this funny look on his face and said "You smell like....girl." Hah hah. I used to use Old Spice. I'm sensitive to the aluminum, but it only affects me if I use it every day, so I only use the Secret every other or every third day.

As for the exercise sweat, I don't worry about it. I mean, I just rode my bike for hours. I should smell.