Aqua Zone is a set of free wargames rules for playing miniatures games that feature underwater combat with submarines, DSV’s and marine animals.
The Miniature Wargaming Editor
Making Terrain From Cardboard
Although this video is focused on Warhammer 40K, I think the techniques shown for building terrain entirely out of cardboard are worth studying.
Faction Wars Science Fiction Skirmish
Fire and Forget Games has released a downloadable PDF version of the rules for Faction Wars, the sci-fi skirmish game. The free 40-page PDF contains the basic rules of the game, sample squads for two factions, and a couple of scenarios to get you started.
Minifigz Lego Combat Rules
Minifigz is a set of rules for combat with Lego figurines.