Well as far as I knwo it depend on what you want to learn about.
Maya comes with a set of books that are good to read as they provide enough information and tutorials.

If you want to model characters fiction/non-fiction you must get some anatomy books, as they will give you much info on how the human character is beneath the skin .

If you want to learn about animation - the Animation Survival kit - is a must as ity provide you the info and the concept of animation.

There are a whole range of books that you can buy for maya (5 of 6) -

If you are a beginner: Maya 6 foundation is a good start if you are new - also Introducing Maya 6: 3D for Beginners
is a good way to get to know the application.

As you stated that you want to learn some organic modeling:
- Learning Maya 6 | Modeling or
- Maya Character Creation: Modeling and Animation Controls

You can also get some tutorials on character animation and modeling.