Mobile Frame Zero is a set of free wargames rules (although you can pay, too, if you like it and can get a printed version) for playing games using Lego and other construction toys. It is very well done.
lego
Brickhammer Lego Wargames Rules
Brickhammer is a set of free wargames rules for playing wargames using Lego and minifigs.
Minifigz Lego Combat Rules
Minifigz is a set of rules for combat with Lego figurines.
Play Ogre With Lego
Steve Jackson’s Ogre is a classic game. I first got a copy when it was in a small bag with thin cardboard cutout counters. It’s gone through several incarnations since then, but the idea of hordes of GEVs and infantry against a single cybernetic tank. Now Dan Efran has a page describing how to build Ogre pieces with Lego. Its really cool, and I can’t wait until my kids outgrow the things and I inherit them.
BrickMech Lego Miniatures Rules
Peter Guenther offers BrickMech, a
d6-based game where Mechs built of LEGO� bricks vie for ultimate control of the battlefield. Constructed in a unique modular system, Mechs can scavenge parts blown off other Mechs to improve their stats. The game is designed to be a rich gaming experience that’s simple to play.