1. Repeat everything they say. Sure it will piss them off but they'll stop fighting with each other.
2. Join in with them and start calling them the silliest names you can think of. Nothing nasty of course, just silly. They'll soon be too busy thinking of other silly names to fight.
3. Leave. They're only doing it to get attention and if they don't think you notice they'll likely stop.
4. Meow. Or bark. Or become a monkey. Seriously. This will either annoy them and they'll leave the room or it will make them laugh.
5. Break out a deck of cards. High card gets to speak for 15 seconds. They'll feel they are being heard.
6. Cry. If you can pull this off they are gaurenteed to feel bad enough to come and see what is wrong.
7. Start talking to yourself. About anything. Your day at work, the cats, the housework. At the very least this will distract them.
8. Give them paper and crayons or markers and ask them to draw whatever they are mad about. This may only work for younger kids.
9. Pray. Out loud. This will work even better if you aren't particularily religious. And if you are well, the guilt factor should work well.
10. Sing. Stand right in the middle of them and sing as loud as you possibly can. Whatever song comes to your mind. Sing loud and proud, even if your singing voice is awful. Actually, that might make it work even better. Stop only when they stop fighting.