The primary function of the core is to prevent movement/rotation in order protect the spine. Therefore, with many of our athletes we implement anti-rotation/flexion/extension exercises. I have also noticed that various others have taken this approach as McGill's research pretty effectively confutes the implementation of crunches/ab circuits/etc. Bare in mind, however, that the discussion as to whether core training is actually required by athletes performing a multitude of compounds is always fierce - it seems to be a seminar/workshop staple.
As for exercise selection; static planks although convenient are pretty awful, however, with little alterations (e.g. adding dynamic movement) these can be made very effective. Conversely, I prefer variations of the pallof press (see: Cressey/Gentilcore), rollouts, uneven load exercises (be careful) etc.
