Make sure you get a book that uses the standard library numeric_std instead of the obsolete std_logic_arith, std_logic_unsigned and std_logic_signed.
As a beginner you don't know that there is a choice for libraries, and they have a big impact on the coding style.
The book by Ashenden is safe.
The Pedroni book I have uses the "wrong" libraries. I hope they have fixed it in later releases.
you can also refer the book VHDL primer by J.Bhasker. It is a basic book,cheap and useful with simple algorithms and examples to start with.
However Peter.J.Ashenden suggested is a good book .But to start with,a simple book is the best option.