William Patterson's DOS port of the classic Intercal-to-C compiler coauthored by Eric S. Raymond.
Catalog of Compilers Intercal Page
Idiom's catalog of free compilers and interpreters mentions Intercal.
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!
Intercal "Hello, World" Program
Surprisingly readable chunk of C-Intercal-only source code written by Clemens Meier.
Intercal Resource Page
Unofficial Intercal language homepage, maintained by C-Intercal implementor Eric S. Raymond. Documentation, implementations, papers, and tools.
Jacob Mandelson's Intercal Page
Featuring a ROT-13 routine and a short link list.
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.
Revised Reference Manual
Compiled from the original specification and from the comments and clarifications by Howell and Raymond.
Intercal source code by Louis Howell.
Malcolm Ryan's proposed standard for Threaded Intercal, version 0.2.
Using Intercal in Perl.