Great and useful book for beginners, anyone who has never used micro-controller can use this book as an introduction to understanding how this awesome piece of the silicon works, then he can move to another complicated architecture easily. Besides that, the book will remain a good reference to you if you work on any project in case that you want to check on the details of a specific point.
it is best book for beginners in the fields of computer science in general and the field of embedded systems in particular. It literally lifted me from the darkness of loss to a good level in understanding how the processor works.
A great book for AVR beginners and expert wanna-be, starts by simple explanation of the computer architecture, goes through programming using assembly and c, With well explained code examples, Enough to learn 8 bit AVR.
NICE BOOK The 8051 Microcontroller and Embedded Systems Using Assembly and C, 2/e by Muhammad Ali Mazidi, Janice Gillispie Mazidi and Rolin McKinlay ( Second Edition , Pearson Education ).