Finding different positions to labor in is all about two things: keeping yourself comfortable, and giving your baby the space he needs to make his way into the world.
This great website has a little slideshow with several different positions that work wonders. I would suggest practicing a little with each of these to see what feels comfortable to you. Of course, all that may go out the window once the intensity of real labor hits, but there's no doubt it's helpful to have some idea of what you want or don't want.
A friend of mine helped me to show you a couple of my favorites:
I am a huge fan of the birthing ball. Or exercise ball, as you probably know it. Sitting on this allows you to hold onto your significant other (or doula, if that person is absent) and simultaneously get your back worked on.
It's also perfect for the end of labor, when you are exhausted and not wanting to move at all. You can roll around and keep your hips moving without breaking a sweat.
And there is one final position I didn't quite get a picture of: laboring on the toilet. This one does not create much movement, but it allows you to relax your pelvic floor in a way that nothing else does. You'll need to try to use the bathroom every couple of hours during labor, so while you're there, stay a while. It may be just the push you need to dilate that last centimeter or two.
Try these at home, see how they feel.