Fred Diamond has a simple set of free wargames rules for playing the Indian Wars in the America of the late 19th century.
The Tomahawk and The Flame is a variant of Larry Brom’s Sword and the Flame rules for the American Indian wars 1866 – 1890.
Steve Winter has a nice photo essay of battlefield sites taken during his 2001 trip across the Northern plains. He visited teh sites of the Little Bighorn, Fort Phil Kearny, the Fetterman Massacre, and the Wagonbox Fight.
Tim Greene has a good site for playing miniatures wargames set in the victorian American West. There is lots of information on the combatants, plus battle reports and rules reviews.