Put yoga into any search engine and you will come up with a multitude of resources for those interested in going deeper into the practice. The more I learn and study the more I feel I am just at the tip of the iceberg with respect to the power of our practice. Below are just a few links and ideas for you which I have found useful.
The anatomy related items are my personal favourites. Even if anatomy isn't your thing these images are worth looking at if only to marvel at how incredible our bodies are!
Bandha Yoga is a great resource for finding out about which muscles we use in each pose and how they function. Check out their 3D yoga pose link