Drawing books and DVDs are a very important part of becoming a better artist. They allow you to expand yoru artistic knowledge and learn and practice new skills. Every artist has their own prespective on things, so whenever you read a book on how to draw, you will always learn something new that you did not know before.
Recently, drawing books have been moved into different format - DVDs. This is really helpful. I had to work from books when I was younger, but DVDs are really cool because you get to watch excatly how to artist is drawing something line by line. It's very cool.
Books For Beginners:
Everybody I knew growing up always wanted to learn how to draw Marvel superheroes like Spider Man, The Incredible Hulk, The Fanastic Four and many more. If you really like drawing comins, then thi is a great place to start. You can really learn a lot about form especially forms in action. You will learn the basics that you need to draw great comic book looking artwork.
Christopher Hart is a really cool artist that has created a lot of how to books, especially in the comic genre that are interesting and easy to follow. These are just three of his very cool books. You can always browse Amazon for more of his books like those on Anime if you are interested in that style of work.
Intermediate Level Books:
This was a great book for me. I primarily started in pencil and it still one of my favorite mediums to work in. This talks a lot about technique and skills that are needed for doing fantastic pencil drawings. It's not as interesting as the how to drawing books mentioned above, but it will give you a solid foundation of pencil techinque and will expand your skills if you have been drawing in pencil for a while.
A fanastic book written by Betty Edwards. The book really concentrates on helping you actually see what you are drawing. Being able to see what you are drawing is a true artist gift and is the start of creating great drawings. This book really helped me get outside of myself as an artist and visualize better. Really helps you in understanding proportions much better.
Advanced Drawing Materials:
Scott Roberts DVD videos are amazing. He has a whole series od DVD books on Amazon that you can purchase. Anything from basic persepctive, to how to draw cras, to drawing spacecraft. They are a little more expensive because they are DVDs, but they are 100% worth the price. These DVDs will really help push you to the next level artistically.