book recommendations on FPGA

The Designer's Guide to VHDL, Volume 3, Third Edition by Ashenden is quite good. Others I have found useful are VHDL for Programmable Logic by Skahill and VHDL Made Easy! by Perrilin.

To complement these answers -- there is also a lot to be said for also spending some real quality time with the vendor's data sheets and app notes for the FPGA devices, libraries, and tools themselves. Otherwise you may well miss a beneficial feature or dangerous pitfall of the particular device, library, or tools that you are going to be using, that are often not covered in an introductory textbook. Also devices and tools tend to evolve faster than textbooks can keep up.

See also my old bit on the Art of High Performance FPGA Design http://www.fpgacpu.org/log/aug02.html#art .

1. The first book I would start with is The Designer's Guide to VHDL by Peter J. Ashenden. Assuming that you are already familiar with programming, then this book is good reference to the VHDL language.
2. Next I would continue with Writing Testbenches: Functional Verification of HDL Models by Janick Bergeron. It does not only cover VHDL, but focuses on a number of topics that are important when writing test benches and code for verification. I think it does a better job of emphasizing the difference between VDHL for simulation and VHDL for synthesis than The Designer's Guide to VHDL.
3. After that I would recommend studying the HDL coding guidelines provided by you FPGA vendor. The provide a lot of useful tips on how to write your VHDL code so that it efficiently maps in to the hardware primitives found in the particular device you are targeting.
4. And finally: Download, read, and understand real-world code. I've found the GRLIB IP Library a useful source of inspiration. GRLIB is an open-source SoC library based on the SPARC processor from SUN.