Whatever you do (steps ups, squats, etc) you want to go in the 12 rep range and work on power - pushing as powerfully as possible to mimic the type of muscles used in cycling. The heavy, 6-8 rep sets won't do you much good for cycling. I do like steps ups, as Veronica said, because they are single leg exercises and your weaker leg won't be able to just go along for the ride (tee hee, pun intended.)