HDL

Verilog - Wiki

Tutorial:
Verilog Tutorial from www.asic-world.com
Verilog Tutorial - electornics.com

Reference:
On-line Verilog-1995 Quick Reference Guide
Sutherland HDL

Academic Courses:
MIT 6.111 Introductory Digital Systems Laboratory
Berkeley EECS150 Components and Design Techniques for Digital Systems

Tips & Guides:
A Verilog Designer Guide - doulos

Verilog Tools:
Verilog Tools - asic-world
Icarus Verilog: Icarus Verilog; The Icarus Verilog Wiki