Terrain Thralls has an illustrated tutorial on making a half-timbered, two story roadhouse. The end result is beautiful, and would be useful in a wide variety of settings.
The Miniature Wargaming Editor
JUGS: A Game of Big Stompy Robots
JUGS is a set of free wargames rules for science fiction combat with giant robots.
Giant robots. How can you go wrong?
The Fantasy Trip Compendium of Resources
Metagaming’s The Fantasy Trip is one of my favorite games of all time. It’s one of the core products that drew me inexorably into the gaming world. Here’s a page with a great number of resources for The Fantasy Trip.
Dragon Fight Aerial Combat Rules
Dragon Fight is a set of free wargames rules for aerial dragon combat.
Fokker Fodder
Fokker Fodder is a set of free wargames rules for World War One aircraft battles. The rules are designed for both single battles, and for campaigns.