If you have bad knees and you are not a pussy then here is a good workout, first warm up your legs on the bicycle then start off with leg extensions 30 reps to get the quads ready, then you go the leg press for 20 to 25 reps, after your leg press sets then you squat for 15 to 20 reps and then finish up with lunges.
Only hardcore guys can do a workout like this the lazy gymrats would not be able to finish it.