Hi Darin,
This may not count as core training, but I like to swim. Granted, I'm still a beginner in Kenpo, but I found the Kenpo gave me enough discipline to start swimming again, and the swimming has helped my overall fitness, esp. my cardio.
When my instructor has everyone drop what they are doing and do a series of pushups or situps or jumping jacks, I can actually keep up...which is pretty cool.
Carol