The best results I have ever had for leg power is definitely squats. They put lots of strain on the knees so do them correctly or pay dearly.
Supplimental excercises to squats would be as follows:
Primary power movement= Squats
Secondary power movement= Leg Press
Supplimental excercises are
Leg extensions for quads
Leg Curls for leg biceps femoris or hamstrings
Calf raises for the calves
A typical beginner program would look like this:
First two weeks learn each movement and the proper biomechanics by doing one set of each with a weight you can do for 15 repititions. Do all movements slow and deliberately.
Speed=Injury when lifting weights. Improper technique will get you injured and stop your training.
Once your body is accustomed to each movement the following program used with progressive resistance should be good to start with for beginners.
Squats: 2 warm up sets first with no weight on the bar just to go through the range of motion, second with a weight you can do 15 repititions with.
Squat set 3 will add enough weight so the repitions drop to 10 with 10 being difficult to complete.
Now move to leg presses, your legs are already warmed up from squats so use a weight you can do 10-12 reps with for 2 sets.
Now do 2 sets each on the leg extensions and leg curls with a rep range of 12-15.
Calves are very hard to get to grow so do 4 sets of calf raises in the begining with a rep range of 15-20 per set. You can work your calves every day. They are accustomed to supporting your body all day long so it is hard to overtrain calves.
NOTES: Do this program once every three days. Train one day rest for two. Recovery is as if not more important as excercise. If your muscles cannot recover then they will not improve.
After the first 2weeks of progressive resistance training add one set to your squats and one set to your leg presses with a rep range of 8-10 for the added set.
from week 3 add one set of squats per week until you are doing 5 total sets. Also at week 3 increase to 3 sets of leg curls and leg extensions.
Add extra sets of leg presses on week 4 but do not do more than 5 sets.
Set and rep range should look like this: (After 6 weeks of training)
Squats and leg press: (Not including the no weight stretch and warm up set)
Set1 = 15 reps
set2 = 10 reps
set3= 8 reps
set4= 6 reps
set5= 5-6 reps
Extensions and curls:
10-15 reps for all sets.
All working sets beyond the warmup should be done until you feel as though you cannot do the next rep or until you fail to complete a rep. If you begin to exceeed the recommended rep range it is time to increase the resistance. Get proper instruction before doing the excersizes and check with a physician before starting any serious excersize program.
Do not do squats to failure without a competent partner to assist you.
I hope this will help, remember that you will need to try different strategies to find what works best for you. This will get you started but train with your instincts. You will learn what works and what does not as you go along.