I have a series of exercises that I do at home/the gym for riding:
The Clam (pilates move)
Sideways leg lift
Knee Fallout (good for stretching your inner thigh)
Straight Leg lifts
Using a balance board, practicing sitting position / two-point
Sitting on a Bosu Ball, lifting one leg and practicing balance
Double Knee Flexion (pulling knees into your chest - pilates move)
Spinal Twists laying down,
Figure 4 stretch (legs)
Sideways lunge
Ball Squeeze (put a ball between your thighs and squeeze and hold - then alternate lifting legs)
Leg press
Calf extensions
Those are a number of things that I do...I have more (if you want).