Hiking.
I also do agility with my pups and one of the best things to condition dogs is off leash hiking for an hour + a day. Work up to that of course. Being off leash the dogs can push themselves at their own rate, (most aren't lazy like us humans can be). That's a great base for training.
Also balance training on a yoga ball (they sell special dog balls too) for core training has been very popular.
