My college health teacher told me some tips for that and I have never had problems since....

Warm up, relax, try to breathe as normally as you can, slow your pace, and lastly (the one that helps the most)...She said usually you get a side stich/cramp from having your diaphram out of rhythm.

When you feel that coming on, try to relax, but when you exhale push your stomach inward (think about squeezing a bottle)...I have found this (making sure you are pulling your stomach in while you exhale) seems to get the best results....

Hope this helps...

If you are training just for fitness, recreation, or fun (and not serious racing/athletics), then I say you are probably training at too fast a pace.  For me, when I took Galloway book advice and targeted training at 2 mins/mile slower than what I thought I could do if I really tried, I never again had rib cramps/stitches.   Then, I slowly picked up the pace to get back to where I had dropped down from, but without discomfort or pain.  My rule is that you should not stop because of rib pain or being winded, but because your running muscles tell you that its time, or you are sticking to  a methodical plan.

take that approach and you reach your goals with less chance of injury or the demotivation of  stopping because of pain.

that's what worked for me in going from a ceiling of a half mile to 22 miles. 

I have had the same problem. I figured out to I needed some light food in my stomach. If I ran on an empty stomach it would happen to me. I needed to eat about 30 min before running.  Try it without eating then with eating. I also started using muscle milk with water.  Don't eat a lot just something and drink something as well. Warm up then do your run see if it still happens. That is how I worked it out for myself. Good luck cramps suck.

I use a similar strategy as Runr262.  I think it's usually about relaxing.  I loosin up my my arms and get them further from my body.  Relax my hands.  Take deeper breathes to get more oxygen in the body.  Sometimes I'll slow down my pace and rest my hands on my head to open up my lungs more.

Often I get the cramps if I run on an empty stomach or if I didn't warm up before the run.

If you specifically mean the stitches under the ribs on the right side, here is a great article that explains it:

http://sportsmedicine.about.com/cs/injuries/a/aa053100a.htm

I've tried the thing about always landing on the left foot while exhaling and found it didn't always work. Taking longer, fuller breaths helps sometimes too.

Check your posture.  You are probably slouching in the miles leading to the cramp.  Concentrate on running "tall, quick, and efficient".