I've been to most of the studios in the county. My favorite - BY FAR - is Jamie Surya Yoga Studio in Sparkill. It's worth the drive. Second favorites: Birchwood in Nyack, or Yoga Synthesis in Chestnut Ridge (they also have a Ramsey location). The new Lululemon store has free classes on Sundays at 10 and during the summer, Thursdays at... 5:30? I'm not sure on that time.