Don't care much for how my abs look, I only want a strong core that can stabilize me and prevent injuries.
These works great for that;

Weighted planks / plank variations
Frontlevers
Toes to bar / Leg raises
Lu-bends

anything that engages the lower abs is gold.

Hanging leg raises
L sits
knee ups

also do reverse crunches on exercise ball
and dont forget obliques