I've suffered with IBS for about ten years, I mostly have it under control now although I do have the odd attack. I control it mainly with food, I managed to identify what foods set me off-onions, alcohol, spicy food, to name a few. My state of mind is also a big factor, if I'm worked up or stressed about something it will trigger an attack so its a bit of a vicious cycle.
I found a tablet called "colpermin" which is brilliant. its peppermint oil like oldmarried suggested, but its in a thicker case so the capsule doesn;t dissolve too high up and instead reached further down into ur gut where it is actually needed. Regular peppermint capsules will just release the oil in ur stomach or throat rather than in ur intestines. It takes a while to build up though so wont offer immediate relief during an attack. its vailable from chemists and supermarkets, just in the regular medicine section. usually next to laxotives...!!
Its such a difficult condition to live with as there is no "cure" so to speak, but if you can work out your triggers, be it food, state of mind or whatever, you really can improove ur quality of life. I was told that unless mine was brought under control I would no be allowed my chosen career, so I had to try and figure out a way to make it behave itself. Its not easy though.