I'm going to assume you're talking about exercises for the rider, haha. Squats, lunges, fire hydrants, and calf raises are all great leg exercises. For abs I like sit ups, crunches, Russian twists and planks. For arms: planks, push ups, and lifting weights.
All of these will help strengthen you when done correctly and strong muscles will help you when riding and jumping.
Trotting your horse on a lunge line over ground poles always help work the muscles needed for your horse to become a stronger jumper!!
Cardio is absolutely useful and any exercises that focus on core strength will do the trick :)