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.
related posts
Sticking Point Therapy
Sticking points are much like those really talkative, naked old men in your gym's locker room: you'd rather avoid them! Nothing's more frustrating than making good progress overall but failing to improve on the "big lifts" (bench press, squat, deadlift, military press, etc.)
Tip: Do This BEFORE You Curl
Use the first-tension principle to build bigger, stronger arms. Here's how.
Tip: 4 Calf Training Essentials
What do you do if your calves are small even though you train them three days a week? Try these fixes.
The Lost Art of Overhead Pressing
Build your shoulders and damn near everything else with these “forgotten” exercises. Here’s how.