DnD books (not settings) of older editions that are useful regardless of edition!

[Ralif Redhammer]

Good call! The taverns are full of adventure hooks and flavor. And heck, even if you don't use them, the menus are really useful for making tavern details more interesting.

The Book of Taverns by Frog Games
This is just a series of Tavern locations that can be dropped into any campaign, the great thing is that a lot of thought went into the surroundings and its made general enough to fit everywhere but ensures each location is unique almost to the point where a tavern itself can become a starting point of a campaign.

 

[SerHogan]

THere were a ton of 2E history/resource books - Arms & Equipment Guide, Castles Guide, Celts Guide, etc. - that were great reads on their own for their historical value.