Digital Core Design  
   VHDL, Verilog synthesizable and simulation models.
   http://www.dcd.pl/

Sim-nML  
   A high-level processor specification language. it views a processor as a machine that executes a set of instructions. syntax, image, functionality (side-effect), resource-usage and timing of each instruction are described in a hierarchical form.
   http://www.cse.iitk.ac.in/sim-nml/

Doulos KnowHow  
   Designer's guides and models for VHDL and Verilog. SystemC home. Also Perl and Tcl/Tk for hardware designers resources.
   http://www.doulos.com/knowhow/

HDL at Wikipedia  
   Definitions, resources, and links related to hardware description languages.
   http://en.wikipedia.org/wiki/Hardware_description_language

Ruby  
   Ruby is a notation and design discipline intended for the development of regular integrated circuits and similar hardware and software architectures.
   http://web.comlab.ox.ac.uk/oucl/work/geraint.jones/ruby/

ForSyDe  
   The ForSyDe (Formal System Design) methodology has been developed with the objective to move system design to a higher level of abstraction and to bridge the abstraction gap by transformational design refinement.
   http://www.ele.kth.se/ForSyDe/

Titivillus: Software Development  
   Links to many programming languages, including several HDLs.
   http://tos.maintree.com/titivillus/softwaredev.asp

ABEL Primer  
   Overview of the ABEL Hardware Description Language.
   http://www.ee.upenn.edu/rca/software/abel/abel.primer.html