Erlang's bit syntax[1] is a great for building and breaking up binary
structures. I've knocked up something similar (although a little
clumsy) for Haskell:

http://www.imperialviolet.org/binary/bitsyntax/
http://www.imperialviolet.org/binary/bitsyntax/BitSyntax.hs

I'm sure that this isn't the best possible way to do this, but it
suffices at this stage for many problems.

[1] http://www.erlang.org/doc/doc-5.4.12/doc/programming_examples/bit_syntax.html

-- 
Adam Langley                                      agl <at> imperialviolet.org