yup, do what strengthdawg says, neck curls with bands are awesome, and you can make it as hard as you like. plus if you dont mind the rubber biting you a bit you can even do rotational work with bands that is hard to do with other implements.
the other thing ive done is take two of those stupid velcro ankle straps that every gym has ten of (but no dip belt or neck harness, go figure), undo the velcro and put the hook bit onto the loop of the other, and vice versa to make a big loop with a couple of d-rings around the edge. put a towel round it so all the other gym bunnies dont hate you forever, then put it over your head (preferably make it about the size of your head, duh) and you can do curls, extensions and side bends with a pulley machine. youll love the looks people give you too.
also, do reverse neck bridges, except dont push all the way til your neck is vertical (or you'll probably go too far and end up with your forehead on your sternum, the only time this happened to be was in a collapsed scrum and it wasnt pleasant, dont do it). its more of a static hold but you can get some movement in there if youre strong enough to pull yourself up from faceplant position into half reverse bridge. if not you can use your arms to decrease the load, much like pushing yourself into a headstand.
alright, im a couple beers deep at work on a friday afternoon so that might not make any sense. do neck work! it makes you indestructible