Any kind of cross-training--something that uses muscles that you don't use in running:
Yoga (calms the mind and body)
Swimming - low impact, works every muscle in your body
Resistance training of any kind - weight training, squats, crunches, etc.
Tai Chi
Walking (very different set of muscles than running) Think about getting ankle and/or wrist weights.
Static stretching
Foam rolling for aches and pains
My go-to is fencing. (the sport) It's essentially a marshal art--an excellent full body workout, steadies the mind, and is great cardio!