I bought a stick of the mineral salt deoderant sold at Rite Aid pharmacy after reading about it here on the forums. This stuff is great! Completely odorless (so it doesn't interfere with my cologne) and keeps my underarms fresh for most of the day. It actually keeps me smelling much fresher than regular scented deoderant bars. The only downside is that you have to apply the deoderant liberally in order for it to work properly. You must also wet your underarms with water before you apply it. (It's simply a block of salt)
Anyways, definitely give this a try!