As well as the DebianPolicy there are also some subpolicies. These do not carry the same weight as the policy, but should be followed where they apply for consistencies sake.
Most of them can be found at http://www.debian.org/doc/packaging-manuals/
Notable examples are the perl, java and python policies. Though for the last their is currently a debate about a new version going on. The new version will probably look something like http://people.debian.org/~srivasta/manoj-policy/.