The most effective form of cardio I have found is hitting/kicking a heavy bag alternating with short rest periods(interval training).Another good form of cardio(especially for heavier people) is swimming.I especially like swimming sprints for 20 or 30 meters.
Interval sprinting, sled dragging resited running, and plyometrics. Every once in a while I will incorporate some precore work to apologise to my joints.