I'll just throw some up while I'm here.
Arch-Militant - What it sounds like; consummate warriors who lead the crew into battle, especially during raids and boarding actions. They can be super bad-asses themselves, and also gain leadership abilities.
Pilgrim - Priests, preachers, chaplains, whathaveyou. They can do a little bit of everything except technical stuff, and are especially good at rallying the crew and bolstering morale, as well as fighting demons.
Voidmaster - The sailors, dregs, and squabs who seize the helm, train the guns, batten the hatches, douse the fires, and when necessary fight and die like the dogs they are.
Explorator - Techpriests who handle all the technical jobs too complicated for the Voidmasters. Also have lots of weird Mechanicus abilities that make them useful in odd situations, including investigation and combat.
Seneschal - Bean counters, librarians, spies, and quartermasters. More cerebral than technical, handling any job that involves lots of information. The right-hand, power-behind-the-captain type guys.
Astropath - Wizards and sorcerers who do all the spellcasting type stuff. Their first job is to communicate across space as a living radio, and get lots of communication/scrying powers along with normal mage stuff.
Navigator - Weird specialist sort of psyker who combines some jack-of-all-trades adventuring ability with even more powerful/weak glass-cannon type sorcery.