Thanks for writing us about this. You can see all of our series at http://shop.oreilly.com/category/series.do.
Generally, Head First is a learning series, not always for beginners, but focused on learning new things. You can read about the Head First method at http://www.headfirstlabs.com/readme.php
Our animal books range from beginner to advanced. Within the animal books, many of our more introductory books will be called "Learning XYZ", "Getting Started with XYZ", or "XYZ: Up and Running". More advanced books often have "Programming" in the title.
In a Nutshell books are reference guides.
Theory in Practice books are higher-level books, generally focused on a big idea instead of a particular technology.
And Missing Manuals books are usually in-depth manuals for hardware and software, and there are also some good introductory programming Missing Manuals.
We also distribute books by some other publishers, which you can see at http://shop.oreilly.com/category/publishers.do
I hope that helps!