Star Trek is famous for all of its episodes that have complications due to the 'Prime Directive'. The name itself, however, implies other directives though. Now, of course there are other directives, we are after all talking about a military organization in the form of Starfleet, but I was wondering if there was a 'Secondary Directive' as such mentioned in any ST materials, or if we are just to assume that the remainder are minor directives in comparison to the Prime Directive (and Omega Directive as well).
I don't know that one is ever specifically named; the 'Prime Directive' is, strictly speaking, just the first of the Starfleet General Orders.
Memory Alpha has a good list of them, as well as the related orders and regulations here.
Oh, incidentally, if you accept the Animated Series as canon, there is a 'Starfleet Order 2', just described as being 'against the taking of intelligent life.'