I've just started crossfit training. It incorporates a lot of strength-training movements that train the core along with everything else.

A sample workout:

20 "thrusters" (Hold dumbells at your shoulders, drop into a full, deep squat, then explode up and press the dumbells up at the same time)
20 Vertical jumps (stand in one spot, jump as high as you can, land, repeat)
20 "kipping" pullups (google "crossfit kipping pullup" for a video- these are great for the core because you involve the entire body)
20 (each leg) walking lunges

Repeat 3-5 times, depending on your conditioning (you can adjust reps, too)

Other workouts will go to the opposite end of the spectrum-
8 single repetitions of the deadlift (very heavy with long rest breaks)
...or any other compound movement


Crossfit gyms are popping up all over the place. I'd encourage everyone to try it out, because it's an awesome workout that you can do in a relatively short period of time.