Paschimottasana or seated forward bend asana is excellent for spinal stretch and toning of abdomen. It is benefecial for stretching the hamstrings, lower back and relieves sciatica.
Purvottasana or inverse plank position, is opposite of the above asana. It works on the core and bends backward as opposed to the above asana that bends forward. Make sure that you do not bend the knees and touch your toes on the floor, keeping the legs straight. This asana helps to stanbilize the pelvis and strengthens the legs.
Vasistasana or the side plank position, shown below, strengthens the arms, wrists and shoulders. It stabilizes the core and stretches the obliques. i.e the sides of the waist. It improves balance and focus.