@fBoyle-- I was also going to recommend massage. After a nice massage, when you're neck has warmed up, rotate your head to the right and left and then in circles. Do this slowly because you don't want to make any sudden movements and hurt yourself.
Some light stretching by extending your neck upward is also helpful. And make sure you're sleeping on a nice pillow. I think memory foam pillows are the best for neck stiffness.