Operation Sandtrap is a set of free wargames rules for standard Plastic Army Men.
Army Men: Plastic Conflict is a set of free wargames rules for those ubiquitous 54mm plastic army men. Interestingly, it has quite a bit of flavor background for the game.
Army Men Combat is a set of one page rules for games using the ubiquitous Plastic Army Men.
Brett Drake offers a set of rules called WWII Plastic Skirmish, which are — obviously — rules for playing WWII games with plastic army men.
What more could you want? Your favorite childhood toys. Dice. Mayhem.
The Green and The Tan is a set of fast play rules for combat with plastic army men. I have to say that at first I thought it was about an Irish rebellion.