(EDIT: fixed wrong link)
High Speed Digital Design: A Handbook of Black Magic by Johnson and Graham:
http://www.amazon.com/High-Speed-Digital-Design-Handbook/dp/...
and RTL Hardware Design using VHDL by Chu:
http://www.amazon.com/RTL-Hardware-Design-Using-VHDL/dp/0471...
(the latter for designing for FPGAs)
(EDIT: fixed wrong link)