There are thousands of lousy generators or generators that do not match the style of your campaign. These are the ones that I have found best work with mine. I have not listed wikipedia or Google Image search (as those should be obvious starting points). These generators are fine to gin up something on the fly, however, I prefer to prepare things well in advance. The mapmaking tools are just the first part in the journey - often these generators are used to create an image which is further processed by me in Wonderdraft and then loaded into Foundry VTT.
WORLD BUILDING
Create and curate your own fantasy calendar. Here is the one for the Kingdom of Delthos:
Create weather conditions by looking at historical temperature, wind, and precipitation data
Heraldry Creation Tools | DrawShield
Celtic Currencies
Fantasy City Generator
If you feel like your world building has a long way to go, look at where Midgard is now
MISCELLANEOUS
Generators, in general
JUST FOR FUN
Who the f is my D&D Character
Meatshields! The Classic Fantasy Hireling & Henchman Generator
DUNGEON DELVING
Dungeon Map Creation and Generation
Dunjeon Generator
Exploration time tracking
Secret Door Triggers
Causes of Death (if you find a body)
If you need a TPK to dress out your dungeon or wilderness
Traps and Puzzles
PROP BUILDING
Scroll Generator - best with google Font-family MedievalSharp in 90px bold
Tomes of ancient evils
Public Domain Pictures
Public Domain Art (relating to the Occult and Alchemy)
Maps and Aerial Views of Cities
SPELLCASTING AND ALCHEMY
Herb Generator
New Spell Generator
Pazio’s full list of spells
Scots Gaelic Hymns and Incantations
TREASURE AND MAGIC ITEMS
OSE Treasure Generator
OSE Magic Item Generator (B/X only)
The Tempered Legacy Generator here comes up with some neat looking weapons
Magic Items
ONE SHOTS
Bears Fruit is a solo dungeon module designed for use with Basic/Expert and similar old school games.
One Page Dungeon Generator
MONSTERS
OSE Wilderness Encounter Generator
Enhance Wandering Encounter with up to 100 story options for each OSE monster
Ironsworn Random Foes (Horrors is best b/c of novelty)
Full Monster stats (suitable for PF and 5e D&D)
Pathfinder’s Bestiary
Challenge Rating Calculator
NPC AND PC CREATION
Ironsworn - will generate name, contacts, inciting event
Backgrounds and Prior Vocations
Random Background Generator
Physical Description
OSE NPC Party Generator (B/X)
HEX CRAWLS
Aid for players/GMs to create their own hex maps. Especially useful for a mapper.
Wilderness Hexes to drop in
Shrines
Dark Grim Forest Encounter Generator
Dunjeon Town Generator
Dunjeon Inn Generator (menus, rumors, and more)
Tavern Generator (menu scroll with prices)
Two More
LANGUAGES AND NAMES FOR PEOPLE/PLACES
Proto-Indo-European (PIE) resources
Proto-Indo-European (PIE) translator
An online English-Irish translator (sometimes offline)
An Irish-English dictionary available on Google Books for free:
Irish Ortography (to make sense of the letters used in the dictionary above)
Irish Pronunciation Guide
Capital letters with diacritics are easily copied from this page
Irish Language and Grammar
Irish/Celtic names for PCs/NPCs
Scottish names for PCs/NPCs
Ojibwe (Native American tribal language)
Common to Goblin
Common to Elvish
English to Ancient Greek
Dutch First Names
Gemstones (suitable last names for Gnomes and Svirfneblin)
Anglo-Saxon Dictionary