Recommended book:

RTL Hardware Design Using VHDL

Other suggested textbooks:

Synthesizable VHDL Design for FPGAs

FPGA Prototyping by VHDL Examples

For people who care about clean code:

Effective Coding with VHDL: Principles and Best Practice

The book's accompanying material has a coding style guide that you can get from the link below (included in the zip file), which nicely summarizes the proper style discipline introduced in the book:

VHDL Coding Style Guidelines 

Search avaliable e-resources at Lund University Library.