Here's a very useful book not just for animators, but for anyone who do character drawings. It's called Force: Dynamic Life Drawing for Animators, authored by Michael D. Mattesi.
First of all, this is a book for intermediate and advanced artists. Foundational knowledge of anatomy is required to fully appreciate and follow along with the lessons.
This book is about creating realistic poses for life drawing. Examples show how forces inside the body and outside (gravity or objects) act on the human figure, and how the body reacts to the force.
There are lots of tips and illustrated examples on strong and memorable poses, such as the using of structure and form, overlaps, foreshortening, silhouettes etc. The explanations are clear and simple, even very sketchy illustrated examples bring the point across with very few lines.
While many instructional drawing books teaches how to draw, this book teaches how to think before drawing. Whenever I draw, I always remind myself of the tips to help prevent my characters from being too static.
Additionally, there are also chapters on handling clothing, drawing on location and drawing animals.
There are more pictures of the book on my blog. Just visit my Amazon profile for the link.