Almost all neck pains that come to see me - especially with a stiff neck I give the following exercises.
Cx Retrations:
Neck Exercise Cervical Exercise - Bodyzone.com
And lateral neck stretches:
Physical Therapy Corner: Thoracic Outlet Syndrome — The Nicholas Institute of Sports Medicine and Athletic Trauma scroll down to "Stretching the side of the neck"
If it's causing you significant pain then you should be seeing a therapist. but if you are just feeling stiff then gentle stretching like those I'v mentioned will be ok
Have a good day