If you happen to play a sport that benefits from leg power (try to find one that doesn't – it isn't easy), you will want to take note of the exercises in this article as they will help you reach your greatest potential. There is a difference between having powerful legs and strong legs, though often the two may seem interchangeable depending on your training methods. Powerful legs will allow you to press a huge amount of weight in a short amount of time, basically bringing about a great amount of force and generating that force fast. Your current training may have to change a bit in order to really develop this power, so let's take a look at the exercises line up. The desire is to increase speed and strength, and most of the exercises are not going to be exercises you will want to train to maximum weights. You should choose at least one of them to train as heavy as you can.
Heavy Barbell Squat
The king-daddy of all the exercises, the barbell squat works the entire body, but obviously really focuses on the legs. This is one of those exercises you can benefit from doing either higher rep ranges for muscle endurance or heavy weights for power, and obviously we want the latter for this exercise. For power it's good to go with a medium rep range of 5-8 reps and maximum weights. If you can't do squats it's a real shame, but you can do leg presses...they typically aren't as effective, but you can work with heavy weights and good tempo.
The jump squat is a plyometric exercise, and plyometrics are one of the best ways to develop speed and explosiveness. Try to get as much height on your jump squats as you can. This exercise can be hard on the knees and ankles, it's can be easy to injure yourself if you are not careful when you are performing jump squats. Increase the effectiveness by stretching your arms high as possible above your head. These should can performed without weight or with very light weight (in the form of a weighted vest or ankle weights, etc).
The calves play a big par in generating power, so its important to include them in your training. The key to training the calves for power is being quick on the concentric portion of the exercise which in calf raises is when we press off with the calves, then hold at the top for a moment then lower the weight slowly in a controlled fashion, and repeat by a really fast launch of the calves once more. You can do Seated Calf raises or standing calf raises. Try different foot positioning and if you want a challenge beyond what you are doing already, do them single leg at a time.
Short sprint interval training (SIT) is very hard work, and should only be done on days that you are not doing your leg workouts, or if this is not possible make sure you have as much rest time between the workout and the sprint training. This type of training has great benefits and will definitely increase your leg power and explosiveness. The basic idea is to sprint as fast as possible (max effort) for short distance or time like 10-15 seconds and then rest for half a minute to a minute and sprint again. Rinse and repeat. The idea here is speed not duration.
Try doing these training sessions 2 times per week, but be careful not to over train as these high intensity exercises put a great deal of stress on the body. Eat well too, without proper fuel, you are just damaging your body and not allowing it to recuperate and improve.