Ace---Here are a few exercises that my PT showed me that I've added to my strength workout:

Get a bolster or a large coffee can. Lie down on the floor and put the bolster under your knees. I use ankle weights for this exercise--at first, go light until you get stronger. Slowly raise your leg until it's straight (keep the back of yr knee pressed into the bolster). Count for a couple seconds. You should feel it in your vastus medialis. Slowly lower. Do 15-20 reps, three sets for each leg.

Sit on the floor or a mat. Get a bath towel and roll it up. Put it under your knees. No ankle weights required/recommended. One leg at a time, press the back of your knees into the towel while tightening the muscles in your quads. Your leg should straighten and come off the floor a few inches. Hold, relax. Do as many reps as possible with each leg (until the muscles are fatigued).

You should check out Jennifer Rhodes book. She's a PT and she wrote a great book that has exercises, advice, etc. about avoiding injury. Sorry, I can't remember the title.