For any Maya artist and students wanting to expand their skills and the toolsets at their finger tips to create breath taking art. I would suggest this book, Complete Maya Programming. It is a great book to have in your reference library. The only reference I use more for maya mel scripting is the maya docs themselves.
This book gives simple and complex examples of how to code different types of syntax structure. It's not always the most entertaining read but it is jam packed with great information. A must have.