Cat's Eye Technologies Brainf*** Page - Primarily a list of files associated with the BF language, but includes links to many other resources and a good general stopping point to explore the BF language.
Frans Faase's page on Brainf*** - A very good list of tutorials in BF, including some not so simple programs to try.
Brian Raiter's Brainf*** Page - A concise description of BF, as well as some very useful links. This is also the source of the BF to C comparison.
The Esoteric Non-existent Standards Institute" - A standards (or non-standards... you make the call) organization or group that has attempted to standardize BF. Some interesting documents regarding BF.
CCCC Brainf*** Page - A computer club in Germany has some additional information not found in the other sites, and some interesting documentation. There is also a mailing list link for BF support.
Apache Brainf*ck Module - An attempt to put BF into Apache. Working source code but not much else.
Brain Relax - A BF "compiler" that translates BF code into other more conventional programming languages.