I'm a big fan of the "Perfect Captain" range of free rules not just because of their innovative neatness but also the detailed, immersive knowledge of the periods and spectacular graphic chrome which show they are an obvious labour of love for the subject matter. Oh and did I mention they were free? They ask instead you make a donation to charity for every download but no obligation.
1) "Red Actions" which is for the Russian Civil War and related conflicts such as the Polish-Bolshevik and Polish-Ukrainian wars post WW1 - one of my main interests and Strelets have the figures including the upcoming Polish Haller's Blue Army.
2) Their suite of War of 1812 rules: "Cousin Jonathan" for the larger battles, "John Bull" for the smaller actions/skirmishes and a campaign system "Obstinate Beyond Description" covering the Niagara campaign of 1814. Again, Strelets is coming up with the figures.
3) "A Coat of Steel" are contingent-based rules for the larger battles of the War of the Roses (just as "Lion Rampant" are for smaller contingent/retinue based medieval games - I'm also a fan of those). The USP of ACOS is they make these sorts of battles anything but a boring scrum with everyone just piling in. Must confess I have only a passing interest in the War of the Roses but I'm attempting to convert these to 12th-14th century Japanese samurai warfare for which they would be excellent.