Brainf*** - Introduction to programming in Brainfuck; interpreters written in Brainfuck, Javascript, and C; and links.
Brainf*ck .Net Compiler - Brainfuck compiler that outputs .NET IL code. Includes source of sample programs.
Brainfuck interpreter in PHP - With a short tutorial and some examples to get you started.
Cat's Eye Technologies: The Brainf*ck Programming Language - Programs, quines, an interpreter written in Erlang, and information on source compression.
CCCC Projekte: Brainfuck - Original software, and mailing list. [English and German]
mod_bf - Brainfuck module for the Apache webserver.
Mr. Rock's Brainfuck Pages - Introduction to the language, tutorial, and a Brainfuck to Perl converter.
The Brainfuck Archive - Contains programs, compilers, interpreters, utilities. Sources and compiled versions are available.
The Brainfuck Programming Language - Brief overview, introduction to commands, informal standards for programmers and implementers, and related resources.