In my humble opinion, Marichyasana D (as demonstrated by Sharath Jois in this video) is one of the hardest poses in the Ashtanga Yoga Primary Series.

Ashtanga yoga- Degy practising with me in a Mysore class in my studio in Putney.

David Swenson, teaching first part of the Ashtanga primary series.This clip allows you to really observe the flow of the Sun Salutations. So many yoga poses come from the strength and awareness of the Surya Namaskars. I like the way David teaches the primary series, while it is obviously still dynamic, it is not as fast as some teachers like to practice.

Here is another yoga video that I have come across on Youtube. It is a great demonstration of the Ashtanga yoga primary series featuring John Scott. Enjoy!