The Last Hussar blog has a set of free wargames rules for World War II. They’re a work in progress, so you’ll want to stop back by on a regular basis.
rules
Reasonable Brom
Reasonable Brom is a variant of Larry Brom’s standard rules for the 19th Century.
Republique Napoleonic Rules
The War Times Journal offers a set of free Napoleonics miniatures rules called Republique.
The War Times Journal also offers orders of battle for Jena-Auerstadt, Waterloo, Busaco, Wagram and Dresden.
Legends of the Rising Sun
Legends of the Rising Sun is a collection of special rules and unit lists for using Legends of the Old West/Lord of the Rings rules for samurai. From Wargames Illustrated 278. Direct PDF download of Legends of the Rising Sun.