Not sure if these have already been posted but I watched a couple of them and they're pretty good.
Squat Rx #1: Lower Back Rounding at the Bottom of the Squat
http://youtube.com/watch?v=Rq8CWv8UPAI
Squat Rx #2: GMing Out of the Hole
http://youtube.com/watch?v=wY4gwVlO_k0
Squat Rx #3: Engaging the Glutes and Hamstrings (Part I)
http://www.youtube.com/watch?v=LsoyHoQU4O4
Squat Rx #3: Engaging the Glutes and Hamstrings (Part II)
http://www.youtube.com/watch?v=znPFEAtk8QE
Squat Rx #4: Bar Positioning and Squat Depth
http://www.youtube.com/watch?v=2eZ1HzoH0Rw
Squat Rx #5: Hip & Hamstring Mobility and Flexibility
http://www.youtube.com/watch?v=WKnpmQNhc3w
Squat Rx #6: A Dozen Selected Exercises for Squatters (Part I)
http://www.youtube.com/watch?v=pIECuX8o88c
Squat Rx #6: A Dozen Selected Exercises for Squatters (Part II)
http://www.youtube.com/watch?v=X4NwygdsF_c
Squat Rx #7: Bands and Chains
http://youtube.com/watch?v=vAHvURlC3OA