If you're really new to Linux, and want to know more about Ubuntu, you could try out Ubuntu Manual, for 10.04 (though it's still good for 10.10). It's a nice, basic overview for beginners. The online PDF version is free, but you can buy the book if you really like it.
EDIT: After re-reading your post, and your comments, I have realized this may be too basic for you. Still, there are interesting bits too it even for more advanced users.
When I started with Ubuntu I purchased Ubuntu Unleashed and really thought it explained a lot for me. Still refer back to it for reference occasionally.
This is my favorite book on Linux, called Linux System Administrator Street Smarts. It's also available at Barnes and Noble. It goes through all the linux basics and comes with a lot of practical examples, tutorials, tasks, etc to walk you through using what you're reading, as well as some great ready-made examples for real-life linux tasks (e.g. network authentication, apache configuration, etc.).
I'd suggest the LPI Linux Certification "Wikibook" which you can find here. The book is still incomplete, but already has Basic content which you can surely benefit from. I can assure you it would be one of the best learning sources available, once it is complete. BTW, its completely free! :)
The best real book I have found is UNIX and Linux System Administration Handbook Everyone will learn something from this book. It is awesome.
For Ubuntu specifically, the Official Ubuntu Documentation is fairly hard to beat.
If you really want to get a good understanding of linux, why not build your own installation from scratch?
Since you weren't specific on exactly what part of Linux you are looking to learn it is hard for me to know exactly what to recommend. If you're looking for Linux in general Linux in a nutshell is pretty good: http://www.amazon.com/Linux-Nutshell-Ellen-Siever/dp/0596154488/ref=pd_sim_b_5 Also, if you're interested in the Linux kernel and perhaps how to compile one the Linux Kernel in a Nutshell: http://www.amazon.com/Linux-Kernel-Nutshell-OReilly/dp/0596100795/ref=sr_1_1?ie=UTF8&s=books&qid=1287625440&sr=1-1 If you're looking for the inner workings of google you can quite honestly get a good amount online without books as well. For example: http://www.linuxnewbieguide.org/content/chapter-1-what-linux Or these for more comprehensive topics: http://lotphelp.com/lotp/tour-linux-filesystem http://lotphelp.com/lotp/workings-linux-kernel A search of Google can reveal thousands of sites, as well as books like these. Good luck with your studies!
If you're really new to Linux, and want to know more about Ubuntu, you could try out Ubuntu Manual, for 10.04 (though it's still good for 10.10). It's a nice, basic overview for beginners. The online PDF version is free, but you can buy the book if you really like it.
EDIT: After re-reading your post, and your comments, I have realized this may be too basic for you. Still, there are interesting bits too it even for more advanced users.
When I started with Ubuntu I purchased Ubuntu Unleashed and really thought it explained a lot for me. Still refer back to it for reference occasionally.
Check this post on WebUpd8. It's about 20 great Linux books.
This is my favorite book on Linux, called Linux System Administrator Street Smarts. It's also available at Barnes and Noble. It goes through all the linux basics and comes with a lot of practical examples, tutorials, tasks, etc to walk you through using what you're reading, as well as some great ready-made examples for real-life linux tasks (e.g. network authentication, apache configuration, etc.).
Ubuntu Linux for Non-Geeks: A Pain-Free, Project-Based, Get-Things-Done Guidebook (Author: Rickford Grant)
I'd suggest the LPI Linux Certification "Wikibook" which you can find here. The book is still incomplete, but already has Basic content which you can surely benefit from. I can assure you it would be one of the best learning sources available, once it is complete. BTW, its completely free! :)