A. Loomis

These books are excellent .They were made in the '40s but are still some of the best art instruction books ever written. when I started using them, my figures improved alot. He teaches you how to invent figures when you don't have a model handy and make them believable. He also wrote interesting chapters on composition and technique. My favorites are 'Creative illustration' and 'Fun with a pencil'

you can download some of these books here: http://www.fineart.sk/

Bridgman's life drawing by G.B. Bridgman

How to learn to draw solid well constructed figures.These books helped me learn to give my figures volume and balance. They are also a bit old fashioned in that there is only one body type in his examples, very muscular men and chubby women, the type of figures you can see in Rubens or Michelangelo. His sketches teach you how to simplify and build bodies, almost as if you were sculpting them, and these books are also very useful for sculpting figures. The advantage is that once you can invent these types of figures it is easy to modify them to make more average types.

Perspective for comic book artists by David Chelsea

This is the best book on perspective ever, it takes a dry and forbidding subject and makes it fun. It is written in comic book form, but the lightheartednness does not detract from the fact that it teaches you good solid rules to enable you to draw any scene from any angle.

Drawing animals by Ken Hultgren

Very good advice on how to draw all sorts of animals, with a big part about horses. He shows you how to simplify anatomy and how to draw animals in motion. His sketches are excellent and in a variety of styles from realistic to cartoon. Whenever I open this book it always makes me want to go out and sketch animals!

Drawing scenery : landscapes and seascapes by Jack hamm

This book has been so useful to me. First it shows you about balance and compostion ,and explains how to put together a scene and guide your viewers eye to follow the path that you want it to: follow-through. This is not easy to explain, but he does it very well. Then it goes on to teach you how to draw trees, rocks, water, clouds and just about everything else. there are loads of other books that do that, but this guy shows you how to invent them from scratch and make them look real. This is hard to do and not really written about much. Most books tell you to draw from life or google!