Karnapidasana (knee to ear pose or ear pressure pose) is great for strengthening the spine. It also stretches the shoulders and back. This posture may also strengthen the lungs and can be helpful to stimulate the abdominal organs and thyroid gland. It may also help hypertension and backache.
Matsyasana or Fish pose is one of my (Lesley's) personal favorites. This posture relieves tension in the neck, throat and shoulders. It also stretches and tones the abdominal muscles. I think of this as the "anti-text-neck" pose!