Useful Links and Resources.

Update Jan 2020. Half these links are obsolete/out of date. They will be revised in the imminent website refresh.

VHDL

comp.lang.vhdl FAQ Part 1 with links to the other sections.
Mentor graphics source of the 'industry standard' VHDL simulators Modelsim/Questasim.
Some people prefer the user interface to ActiveHDL to Modelsim if given the choice.
SymphonyEDA, another good, reasonably priced, fully featured VHDL simulator.

Opencores.org
European Space Agency VHDL guidlines (style guidlines)

FPGA

Altera
Xilinx

Why it's important to write specs before you start designing
Andraka Consulting Group Home. Ray Andraka has much experience of pushing FPGAs to their limits and regularly posts on comp.arch.fpga
Burch Electronic Designs

Atmel's combined AVR core and FPGA fabric - FPSLIC

Hardware - Design

High Speed Digital Design, Howard Johnson, an excellent text on high speed dital design (not this link is to Amazon UK).
AnaSoft- Mixed-Mode Analog Simulation with Schematic Capture and Filter Design (a spice variant with good front end)
PCBStandards.Com An excellent resource for PCB design, standards, PCB design checklists, BGA routing papers etc.
Designer's Den - A PCB Designer's Page
'The Scientist and Engineer's guide to DSP", downloadable version of this very readable book.
Kimmel Gerke Associates, Ltd.
Some interesting input/output signal conditioning (wrt EMC) stuff (in magazine articles section)
CapSite 2000 - Technical info on caps

Some good Metastibility resources.
Leroys Engineering Web Site; MetaStability
Metastability Discussion
Discussion by Howard Johnson, author of 'High Speed Digital Design' (see above).

Hardware - Manufacturing

PCB POOL. By combining customers prototypes with similar technology requirements into larger boards set up costs are reduced. We have had excellent results from PCB-Pool and have used them for most of our PCBs.
Stewart Technology - Contract electronic manufacturing company based in Galashiels.
Border Circuits, a PCB manafucturer also based in Galashiels, specialising in fast turnaround prototypes.

Some other manufacturing resources
AP Circuits a Canadian based PCB manufacturer (we've had one board from them and were pleased with the results)
Newbury Electronics - Newbury (UK) based PCB manafacturing/assembly company
Advanced Circuits - Printed Circuit Boards
Allgood Technology - UK based SMT assembly specialists

Perl

Active State, you can download the latest version of Perl from here. Active state also provide the Perl packages (such as the Tk graphical file extensions). Look under http://www.activestate.com/PPMPackages for the packages for the version of Perl you are using. As of Feb 2003, we'd recommend downloading ActivePerl 6XX as most packages are available for it.
After a recent Perl installation on new machine we had problems installing the Tk package. Uninstalling Perl and re-installing with PPM3 disabled sorted the problem, Tk.ppd and Win32-Api.ppd installed cleanly. This is worth trying if you encounter any problems.
CPAN - Comprehensive Perl Archive Network, good for links, FAQs and documentation.

Robert's Perl Tutorial, a good overview and quick start quide.
Beginning Perl is a a readable introduction that thoroughly covers the basics (and more).
The Camel Book is known as the Perl book.
Learning Perl/Tk: Graphical User Interfaces With Perl. A very useful reference when starting to build GUIs.

Usenet

Usenet is the often overlooked aspect of the Internet. It consists of 'Newsgroups' which are (mostly) text based discussion groups on every subject under the sun, from motor cycle maintenance to sewing, run like bulletin boards. Although the messages 'expire' after a certain period they are archived, and this archive becomes an incredibly useful resource. If you're stuck trying to work out how to do something a quick archive search turns up the solution more often than not. To see more visit http://www.google.com/grphp and enter the subject you're interested in, or navigate through the hierarchy to find specific groups.

Useful groups for FPGA and hardware design include comp.arch.fpga, comp.lang.vhdl, comp.arch.embedded and sci.electronics.design.

For VHDL try comp.lang.vhdl.

Google's a great resource, but for keeping up to date with current topics there are better newsreaders. I like the newsreader integrated with Netscape; Outlook Express also isn't too bad. Search for 'Newsgroups' in their help files for details on how to set these up.

Miscellaneous Resources

QVCS - Qumasoft Version Control System, a compact version control package ideal for small companies/teams/personal use.
Prestosoft - The home of Examdiff an excellent free visual file comparison tool (this can be set as the default when doing version comparisons with QCVS.
Ganssle Group - Discussions on embedded system design (mainly from a software viewpoint)
Beyond Logic - Great resource for all aspects of PC interfacing (hardware to device drivers)
AVRfreaks.net
DonTronics Home Page - AVR, PIC and other prototyping resources.
Richard Steven Walz's WWW Home Page
Message boards for professionals and traders in the electrical and electronic industry.
An extensive set of Robotics related links

BCBDEV.COM - My second port of call (after a usenet search) for C++ problems.
RS
Farnell

Dilbert - Who hasn't come across a pointy haired boss?