Brian Raiter's INTERCAL Page has a lot of INTERCAL related documents, including the original INTERCAL-72 specification. He also wrote a couple of INTERCAL programs and libraries, including a floating point library as well as the first (and probably last) pure INTERCAL CGI program.

The INTERCAL Resource Page is another good page with lots of INTERCAL stuff. The page is maintained by Eric S. Raymond, the author of the C-INTERCAL compiler.

The Pit is an INTERCAL Page maintained by Louis Howell, one of the top C-INTERCAL hackers. He maintains a fairly large collection of INTERCAL programs, including Conway's game of Life and programs to calculate prime numbers or digits of Pi.