Calendar that not only shows the date and month but weather, holidays, important events from history and religious observances (all or most hyperlinked or referenced to get more details).
Adventures and adventure idea's.
Unique or notable locations with histories and rumors attached.
Rumors and news about what is going on in the world, fashions and trends
Notable NPC's, Monsters, Organizations and sects.
New feats, classes, races, skills, Prc's and what classes, races and Prc's from the core rules would work in this campaign with examples of how they fit in the world.
Encounter tables, weather generator, NPC name generator.
Interactive map that allows me to point and click and get information about that area.
Easy to navigate.
Articles by the writers about the setting and the feel they were trying for as well as more details about the campaign that they wish to expand upon or was cut from the production campaign.
Things that help me to broaden the feel of the campaign such as vocabulary and common sayings, governments, fashions, Dieties, regional histories and events, race and country interactions/attitudes, unique observances, basically things to spawn the imagination or guide without forcing changes like Meta plots.
Fiction professional or submitted with details about the characters and places involved in the writing.