for me i tend to do heavy barbell shrugs with a slow ecentric (lowering) part. For variety i do heavy dumbell shrugs with the dumbells in line with my feet (ie at my sides).
Not 100% about this one tho but i was reading about some training regime that uses only body weight exercises (i know your thinking what for?) but it was a routine for an ultimate fighter type dude. One of the exercises was called a 'back bridge' basically you plant both feet firmly on the ground and than arch your body backwards till your forehead is on the floor. Guess its a variation of what some old school wrestlers would do. Can see that something like that would put a bit of strain onto the neck and back.
Maybe when i lose some of this excess weight ill give it a try but for now <shrugs> heh