Your favorite in-game D&D organization

[zztong]

The Harpers (Faerun) could be really neat, or they could be cheesy, depending on how they were portrayed, but I did like them.

I once portrayed both the Blacklock Loreseekers (Faerun) and later the Pathfinder Society (Golarion) in a homebrew game as a bunch of old stuff-shirts who overly embellish and exaggerate their deeds. They would also sponsor poorly thought out missions using dandies and incompetents that would end in failure, but then be turned into glorious pulp novels that sold well. The PCs would find their bodies on mission after mission as a running gag.

 

[Chad Hooper]

I may well steal that pulp novel idea, that sounds absolutely brilliant!

 

[Legatus Legionis]

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[Shasarak]

I like the Red Wizards, not just a monolithic entity but an organisation broken down the lines of magic schools competing with each other.

The Zhents are quite interesting as well.

 

[Eltab]

Fzoul Chembryl's Zhentarim were much more interesting than the 5e faction version.

Manshoon's version inspired how I portrayed the Cult of the Dragon in my Tiamat campaign.
(I had the Classic Cultists look askance at the living dragons.)

 

[Yaztromo]

I like the Brotherhood of the Radiance, in Glantry, Mystara.

I like the fact that it is an overpowered, but higly secret organization (Rad himself is part of it!) but at the same time it brings a lot of danger (Radiance disease, possible assassination between Brothers, it is an illegal association in Glantri, researching Radiance spells and receptacles is very difficult and expensive...) and, with a bit of luck, it is a possible way to immortality!