Ok, just popping a few of the best one's up on here, as they're one's that most people would use every time they play (ish):

This first one is a must for all who want to get involved in the economy. Has everything from raw materials, structures needed, overall cost of complex items:
Production Cost Analysis (direct download ~ right click, save target as)


Great guide in getting a look at how ship outfittings change your base ship chats before you actually buy them:
Ship Outfitting Calculator


A file of all base ship stats:
Ship Stats (direct download ~ right click, save target as)


A file stating all the ship outfitting stats:
Ship Outfitting Stats (direct download ~ right click, save target as)


A nice online map that helps you get an idea where missions are located on the map:
PotBS Google Map


The atlas is a bit different to the above map, mainly as this is a searchable one, allowing you to look up raw materials in ports. Another must for economy nuts:
Atlas of the Burning Sea


Does exactly what it says on the tin, the server status page:
Server Status


This is the PotBS Europe site. If you're on one of the EU servers, this is where information regarding game events and such are all stored:
PotBS Europe


An indept guide to combat mechanics, goes into a LOT of specific detail regarding every aspect of combat, written by a dev of the game, Taelorn:
Combat Mechanics


Guide to how the existing reputation system works in PotBS:
Guide to Reputation


The fountain of knowledge that is PotBS Wiki. Lists all missions in the game, locations, societys... everything really:
PotBS Wiki


A file that allows you to calculate the exact distances to ports:
Distance calculator