I have suffered VERY severe cramping for around a year now. The cramping causes me to miss work, curl up in a ball on the floor in a fit of anguish and wish I was dead, 3-4 times in one day for the first few days of the cycle. I have had other side effects, such as profuse clottage (sorry for the grossness) and fainting spells. I have gone to the doctor about it, but he merely suggested I go on birth control pills, after admitting that the pill wouldn't solve the problem, just take away the symptoms until I come off the pill. But, from my extreme moments of pain, this is the advice that I can offer.
It seems to help if I stay away from eating too much red meat, as long as I eat enough to keep a certain level of iron. Staying hydrated and well-fed helps also. Ibuprofen works well, although it is more of a preventive measure than anything. Meaning: it may not work unless taken before you start feeling the cramps. DO NOT take more than the recommended dosage of ibuprofen, even if it works better that way. Before I discovered Aleve, I took somewhere around twelve 200mg tablets daily. It saved me the horrors of the pain I felt, but it probably rendered one of my kidneys useless. Someone mentioned doing sit-ups. Being well toned may help, but I can't imagine doing sit-ups during cramps. If it works for you, go for it. Back massages certainly help. I have found that allowing myself to be irritable increases my unhappiness, and thus, increases the pain. So if there's any way to put yourself in a good mood, by all means do so.