This exercise brings the rib cage and pelvis together to give the obliques a good squeeze.

Oblique Crunches
Step 1
Lie on back, with knees bent.
Step 2
Cross left ankle over opposite knee.
Step 3
Place right hand behind head and lift right shoulder toward left knee.
Step 4
Release down. Do 5 to 8 reps, then switch sides.

Source: Parenting