Muppet Lab's Intercal Resources
Features the original specification and a sample source code collection. Links to several compilers and to other Intercal-related sites.
http://www.muppetlabs.com/~breadbox/intercal/

Jacob Mandelson's Intercal Page
Featuring a ROT-13 routine and a short link list.
http://www.ofb.net/~jlm/intercal.html

Revised Reference Manual
Compiled from the original specification and from the comments and clarifications by Howell and Raymond.
http://www.muppetlabs.com/~breadbox/intercal-man/

Intercal Resource Page
Unofficial Intercal language homepage, maintained by C-Intercal implementor Eric S. Raymond. Documentation, implementations, papers, and tools.
http://catb.org/~esr/intercal/

iperl
Using Intercal in Perl.
http://catb.org/~esr/intercal/iperl.html

Intercal "Hello, World" Program
Surprisingly readable chunk of C-Intercal-only source code written by Clemens Meier.
http://www2.latech.edu/~acm/helloworld/Intercal.html

The Language from Hell
Article and site, non-fiction, and journalism indexes.
http://www.antipope.org/charlie/journo/intercal.html

Threaded Intercal
Malcolm Ryan's proposed standard for Threaded Intercal, version 0.2.
http://www.cse.unsw.edu.au/~malcolmr/intercal/threaded.html

Catalog of Compilers Intercal Page
Idiom's catalog of free compilers and interpreters mentions Intercal.
http://www.idiom.com/free-compilers/LANG/INTERCAL-1.html

C-Intercal Compiler
William Patterson's DOS port of the classic Intercal-to-C compiler coauthored by Eric S. Raymond.
http://www.komputado.com/iloj/diversaj.htm#intercal

The Pit
Intercal source code by Louis Howell.
http://www.ofb.net/~jlm/howell.html

INTERCAL
Urban Nilsson's collection of INTERCAL programs.
http://www.oops.se/~urban/INTERCAL.html

Darren's First Intercal Program
This was author's first exercise in INTERCAL programming. It counts down from 500 all the way down to one. It's that simple!
http://webonastick.com/intercal.html