A bit off topic, but my favorite stroke videos are:
(1) Tennis Guru's Restrung In 24 Hours DVD: http://www.**********.com/
(2) Millennium Forehand: http://www.virtualtennisacademy.com
(Not a fan of the straight arm or how the lady turns her head as she does the unit turn, but it's ok.
I like Jeff Salzensteins work. I was able to immediately use what I watched, and my positioning immediately improve. Other players commented how I seemed faster... His total tennis membership is only like $10: http://www.jeffsalzensteintennis.com