Culled from many forum threads and my own experiences, this is one strategy for creating a city/government to produce powerful military units quickly.

City Placement and Improvements

Grassland with 6 or so farms (creates surplus food so hill tiles can be worked)
Plenty of hills to mine
Helpful resources: Copper, Iron, Aluminum, Coal (+3 production each), Horse, Cow, Oil, Stone (+2 production each)
Railroaded mines (+1 production)
Aiming for an ultimate population of 20 (to work every tile, plus city tile)

Buildings
Barracks (+4 xp land units)
Drydock (+4 xp naval units)
Forge (+25% production)
Factory (+25% production)
Power Plant (+25% production)
Jails (optional, -25% war weariness in their city)
Health: 20 for population, + extra for factory, power plant etc... (Get from: resources, granary, harbor, grocer, aqueduct, fresh water, hospital etc...)
Happiness: 20 for population (Get from: resources, Forge+gems/gold/silver, theater, temple(s), market, military units, colosseum + culture slider etc...)

National Wonders
West Point (+4 xp) National Wonder
Heroic Epic (double military production speed) National Wonder
Use Red Cross National Wonder in another city to produce some defensive units, as medic bonuses don't stack

World Wonders
Pentagon (+2 xp) World Wonder
Three Gorges Dam (free power on continent, for extra production) World Wonder
Mt. Rushmore (-25% war weariness)

Civics
Aggressive leader (free Combat I promotion, half cost Barracks/Drydocks), includes: Montezuma, Napoleon, Alexander, Huayna Capac, Tokugawa, Genghis Khan, Kublai Khan
Vassalage (+2 xp)
Theocracy (+2 xp)
Police State (+25% military production, -50% war weariness)
Emancipation (No upkeep, offset high upkeep civics)
State Property (No upkeep, offset high upkeep civics)


Unit promotion totals: Combat I freebie plus 14 xp gives you 3 promotions to hand out right off the bat. Only 3xp is needed to get the next promotion as well.

Note 1: Building a city in this form is helpful in many games, even without any of the listed civics or the Aggressive leader trait, because you can still get powerful military units produced quickly.

Note 2: Jails/Mt. Rushmore/Police State are suggestions if you plan on warring most of the game, which if you choose an Aggressive leader and these civics you probably should be ;)

Let me know if I missed something or you have more ideas for this kind of military production city in general. Or in a larger scope how you choose to run warlike governments.

Mostly possible by two EXCELLENT threads by remconius: A guide to city specialization (http://apolyton.net/forums/showthread.php?s=&threadid=143432) and Building Elite Units (http://forums.civfanatics.com/showthread.php?t=141264). Thanks for all your insight!