Two good sources for fantasy government: Plato's Republic and Gary Gygax's original ("1st Edition") Dungeon Masters Guide. The DMG just had a list of government types, but you can look them up online to learn more.
Some of the more interesting ideas:
-- Timocracy -- rule of the brave in Greek. You can see this form of government in the "Starship Trooper" movie: "Service ensures citizenship". The basic idea is that only veterans can vote or serve in office. Plato thought this would be a good form of government, whereas Paul Verhoeven (director of "Starship Troopers", "RoboCop" and "Soldier of Orange" about his native Netherlands under Nazi occupation -- all meditations on fascism) thought it would be a vicious, warlike regime that lies to its own people to justify war.
-- Syndicalism -- Rule by guilds/unions. Anarcho-syndicalists (believing in no government other than by the workers in their own shops) actually did have a real movement and controlled some areas of Spain during the Spanish Civil War, until their best (elected) general was assassinated by their Communist allies. This bizarre but real(-ish) form of government has good fantasy roots. Remember the lines from "The Holy Grail":
"We don't have a lord. I told you, we're a self-governing anarcho-syndicalist commune. We take it in turns to be a sort of executive officer of the week, but all decisions of that officer have to ratified at a special bi-weekly meeting, by a simple majority in the case of purely internal affairs, but by a two-thirds majority . . . "
"Be quiet! Be quiet! I order you to be quiet!"
"'oo does 'ee think 'ee is, giving orders?"
-- Divine Mandate -- enough people have claimed it, why not have it as a real form of god-appointed leadership in a fantasy game?