Other than actually activating your core (and shooting for intensity over duration), the key to making planks not suck is to keep your mind busy, whether that's lifting limbs, walking around, or moving weights.
This exercise will hammer the trunk when you maintain a rigid plank. And once you've got that down, you can raise the difficulty by increasing the load or moving the weight in front of the hands.
One of my favorite books is A Book Of Five Rings by Miyomato Musashi. Musashi was a badass 17th century Japanese swordsman who never lost a duel in over sixty fights. This book outlines his philosophy of success. I re-read it recently and was amazed by how many of his principles apply to a variety of areas in life, including productive strength training.