Best CORE EXCERCISE EVER! : Fork Put Downs.

          But in all seriousness folks. This is the one thing that was the hardest for me to tell all my clients. They would come to me looking for strength, power, and the ability/movements to give them a super flat/6 pack stomach... I was always honest and told them the stomach they were looking for wasn't in the gym... it was in their own kitchen. I would still work core with them tho promising them that when their diet and training were on the same page and consistent; that they would be more than happy with the results. So that it my rant for today, now lets focus on that core and PRACTICE PRACTICE some difficult movements.

Planks Enforces proper posture and hip stability/mobility.
Side planks. Work the obliques (if done correctly), and apparently are good for hip mobility too. Add the leg raise for extra fun.
Ab-wheel roll-outs (kneeling or standing). Excellent anti-extension exercise. The kneeling ones get easy pretty quickly, so you'll need to add weight/do them on an incline to progress to standing ones.
Hand walkouts. These are similar to rollouts, but you don't need the wheel. And probably easier to progress.
Hanging leg raises With straight legs, touch the bar with your feet and make sure you actually bend at the spine, else its just a hip flexor exercise. These feel great if done correctly, and also work your grip a little.
Dragon flags. These give me the most intense contraction of all the exercises I named. Also added bonus of anti-extension.
Pick one or two (preferably one plank, and one of the dynamic ones), and work on that after your regular workouts, 3 times a week. More often if you are a beast.

Today isn't a super heavy hard day. But make it a practicing day for what ever skill you would like. Tomorrow will be a much deserved rest day if you hit today hard enough. Get ready for next weeks cycle!