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.
The Miniature Wargaming Editor
Alan’s Landship Game
Alan’s Landship Game is a set of free wargames rules that pits Victorians against Martians.
Reasonable Brom
Reasonable Brom is a variant of Larry Brom’s standard rules for the 19th Century.
Autokill Auto Combat Game
Autokill is a set of free wargames rules for vehicular combat.