Hammerstrength makes a pretty good neck machine. It will train all 4 angles. You will need to find a well equipped gym to find a neck machine, however. Most don't have them.
Some gyms have a special harness which you strap onto your head, and has a chain leading to a hook from which you hang weights or attach to a cable machine.
Go here and have a look at some of the possibilities for neck training. They have little videos for illustration purposes:
http://www.exrx.net/Lists/ExList/NeckWt.html