For what it's worth, I'll throw in my two cents. I have the same problem, my orthopedic surgeon basicaly told me no squats or lunges, though doing wall squats with a stability ball is okay. Try to limit high impact cardio b/c overtime it'll only make the problem worse. I didnt heed his advice...and he was right! To help strengthen the knee area he recommended quad strengthening exercises that keep the knee joint straight such as straight leg lifts with ankle weights. And, to counterbalance, it is important to incorporate hamstring stretching. I found yoga with its downward dogs to be great for this. I have much less knee pain if I do planks with my elbows bent instead of with straight arms.