I’ve been doing this for five years now, so there’s a lot of material here. If you want to cherry pick and just look at the very best, here’s the ones that people keep coming back to, in order of descending popularity.
Wizard’s Spellbook Generator for Pathfinder, 1st edition, c2014: A set of Excel sheets. Hands-down the most popular download so far.
Selling Wizard’s Spells in Greyhawk, Pathfinder Style: Can you tell I often play a mage?
John Eric Holmes, Confessions of a Dungeon Master (1980): A classic article from Psychology Today that is really hard to find nowadays.
Ruined City Generator: Just a page that sends you to the efforts of other folks.
Gamma World Cryptic Alliances Redefined: A non-canon revision of the Cryptic Alliances, drawing from all editions of the game.
Trying to Map Middle Earth: When we started playing MERP again, I tried to put together the most awesome Middle Earth map ever. Here’s why I failed, and some great resources that might help your effort.
Iron Rations in D&D & Pathfinder: Trying to figure out where that term came from.
The Play is the Thing, pt 1: A three-part discussion of role-playing.