this post over on Eli Arndt's most excellent I See Lead People blog and it really piqued my interest. The idea behind The Galactic Trade Authority is simple: An organization that provides protection for trade ships and depots for a price. Initially created by an alien race called the Nawleen to secure their own interests, the GTA soon extended its services to other alien races and eventually was officially endorsed by the galactic government to act as a pan-galactic agency. While the Arndt created the GTA for wargaming, its a concept that can easily be employed in worldbuilding.
Scenario: Piracy is rife in the galaxy and the major powers/galactic government is either unwilling or incapable of handling it adequetly. A group of corporations or trading guilds decide to take action and form a body to protect their convoys and trade centers. The organization soon grows in reputation as more and more companies enlist their services until the government(s) promotes it to that of a government entity. You could even have it where the agency becomes corrupt overtime due to political patronage or just straight up bribery.