*) Starter's Guide to Verilog 2001 , by Michael D. Ciletti
*) System Verilog for Design (2nd edition), by Stuart Sutherland etc.
*) System Verilog for Verification (2nd edition), by Chris Spear
*) Verilog Designer's Library, by Bob Zeidman
If you use VHDL,
*) The designer's guide to VHDL (3rd edition)
For CPLD/FPGA device
*) Designing with FPGAs and CPLDs, by Bob Zeidman