I'm doing the workouts in "New Rules of Lifting" and it has a two point stance on the subject:
1. Stabilization, coordination and balance. For this, moves that require effort to stay in place: Swiss-ball lateral rolls (fiendishly hard), supine hip extensions w/ and w/o leg curl.
2. Strengthening through flexion: swiss-ball crunches, reverse crunches, incline reverse crunches, russian twists.