Got the flu late last year and started tabletop gaming, to make a long story short. That is, I started collecting the miniatures but still haven’t played a single game. But at least they’re cool to look at.
Anyway, before I went and gave all my money to Games Workshop, people recommended BrikWars to me. All you need is a bunch of toys or small objects, preferably LEGO, and a couple of six-sided and one 20-sided dice. The Rulebook has been around since 1998 and is so nicely done, it puts commercial wargaming systems to shame (it’s free btw). If you’re still sceptical about the amounts of fun that can be had with such a simple setup, take a look at this battle report.
BrikWars is a marvelous Pandora’s box, an endless fount of destruction and mayhem, where every coincidence falls in favor of maximum violence, where life is cheap, plastic, boxy, and bears only the most superficial resemblance to our world of flesh and mortgages. Time is marked from moment to moment by oscillating peaks of melodrama and troughs of sheer ridiculousness. (BRIKWARS 2005: The BrikWars Universe)
EDIT: BrickArms sells weapons and modifications to give your toys that extra-militant look.