I have heard of using a little mouthrinse... but I have used the o'neil wetsuit shampoo- just soak the suit in a tub or something with cold water and some of the soap- or any wetsuit shampoo with conditioner and it will work wonders- seriously the stuff is like gold. not only makes the suit smell new- but it feels new too!!!
I at least like to give each suit the shampoo at the end of its respective season, before I put it away for a few months. Sadly, I fear that day is rapidly approaching for my 3/2...not yet though.
What makes a wetsuit stink is mold spores locked into the neoprene. The reason this happens is because even though you think your wetsuit is dry it really isn't completely because of being in salt water. The salt actually keeps it damp. The best way to avoid a stinky suit is to wash it thoroughly with fresh water. I usually fill the tub with warm water and just plunge my suit in and out for a few minutes and then rinse repeatedly under the faucet. After rinsing you have to hang it up to dry. You want to try to hang it where the air can get to it but not in direct sunlight. If you keep it inside out it will dry better and also won't fade. Like I said keep it out of the sunlight because it will do all kinds of damage to your suit. Been doing this as long as I can remember and have never, ever had a stinky suit.