Judge's Guild was founded in 1976 and published such classic Dungeons and Dragons and generic RPG materials as the Ready Ref Guides, the City-State of the Invincible Overlord (the first city based RPG setting!) and the infamous Tegel Manor module. After many ups and downs, Judge's Guild has recently reappeared on the RPG scene, offering .pdfs of its classic products for sale as well as the promise of new material in the near future.
http://www.judgesguild.org/