Yeah I'd second Australia.... While I'd never argue it's significant enough for a mainstream out-of-the-box civ, it's small but disproportionate impact in 20th century warfare, politics and culture relative to it's size makes it a legitimate second tier civ for any mod dealing with a modern era much like the often mentioned Poland, Brazil etc.
For UU choices I've gone with a slight tangent on what you might expect from an Australian Civ (in past Civ games, any Australia Mod has used the Australian Light Horse or a worker unit pretty much)
UU1 is representative of 20th Century military experience almost exclusively on foreign territory (WW1 France/Flanders, WW2 North Africa/South Pacific, Korea, Vietnam etc notable in defensive or counter-offensive actions)
UU2 is less notable historically but still accurate enough and provides flavour since there are very few if any Gunship UU's in the game. When engaged in Vietnam, the RAAF as with the Americans flew the ubiquitous UH-1 Huey... the difference was with the variant they employed in the gunship role, packing two fixed forward firing M134 7.62 mm miniguns (one each side) and two 7 round rocket pods (again one each side) - considerably greater firepower than their American counterparts were packing in a standard Huey gunship at the time, something noted by ally and foe alike in that conflict and more widely representative of the historical tendency of Australia's military to take a piece of kit and modify the bejesus out of it...
The Leader could be a toss-up of any three (Barton as Australia's first PM, Menzies as it's longest serving PM or Curtin as it's wartime PM during the only time the country's territory was directly threatened and breached by a foreign power)... I've gone with Menzies.
UA is chosen pretty much because Australia has always been a middle tier economy, able to thrive because of it's nature as a Primary Economy (ie one based on natural resources) supplying resources to trading partners (from the UK in it's early days, to China and India today).
Civ: Australia
Leader: Robert Menzies
UA: Resource Rich: Mines and lumbermills provide 1 extra shield
UU1: AIF Infantry (Replaces Infantry), +25% defensive bonus outside of friendly territory
UU2: RAAF Gunship (replaces Helicopter Gunship), starts with Logistics