I just lie on my back, and stretch my arms and legs out as far as I can and then hold it for several seconds, relax, repeat. Looks retarded but works very well.
Another one is where you sit (upright)on the floor, extend one leg fully, and then bend the other leg at the knee and cross it over the extended leg, you then twist your body in the same direction as you crossed your bent leg (after that you do the opposite to complete the stretch)- sounds complicated but I don\'t think I\'m describing it well. My doc gave me a pamplet of back-stretches (they\'re diagrammed), I\'ll see if I can get my hands on a scanner at school.
Using the exercise ball Videoholic mentioned is another excellent way to stretch your back.