Amazon’s first day of their Twelve Days of Deals features a lot of games. Lots of stuff for Imperial Assault, X-Wing, Descent, Zombicide, plus board games like Dominion, Potion Explosion, Terra Mystica, Letters from Whitechapel, Suburbia, Smash Up, and on and on.
All at the link are at least 25% off as of this writing.
Strike Force One is designed as an introduction to the hex and counter genre of board game.
Law of the Gun is a set of free wargames rules by Richard Bradley for Wild West Skirmishes.
Fornovo to Sedgemoor is a set of free wargames rules for Pike and shot rules for the period 1485-1685. The rules are designed for 15mm – 30mm figures, on a 1:25 scale.