Lunges! Great exercise for cyclists. Do them forward, do them backwards, side to side, out to an angle and back to an angle. Do them across the lenght of the gym, do them to a press as you go across the gym, do them with light weights and progress to heavier weights. Watch your form! Don't bend at the waiste. Take deep steps no matter which direction you're going. Do 10-15 reps per leg per exercise and even do 2-3 sets. Maybe pick 3 or 4 of the above options at each training session. Do them year-round, not just during the winter months.