Cassey Ho - Blogilates -
Find it on: YouTube
My favourite of Casseys workouts are her extreme abs collection.
Tony Horton - P90X
Find it on: Paid Subscription
P90x is high intensity and gives you a serious workout. Perfect for cold and rainy days when you can't go workout outside, you will get a serious workout from this.
my personal favourite of all the videos is the plyometrics workout.
Shaun T -Insanity -
Find it on: some on YouTube, most subscription
Insanity is in the same ball park as P90X. high intensity, real hard work. You will get a serious workout with these videos and the collections offers videos to suit what ever type of fitness you are after.
Be warned, this is some advanced fitness, but it will result in some serious gains.