The Agromancers. The are Autobots who transform into agricultural machines. I'm surprised no one has thought of this yet. Barnpicker: is a red tractor. He's much like Cybertron Landmine. Turbo Haul and Rumblestack combine to form a John Deere combine harvester. Steamcrusher is a Decepticon that transform into a tank
Apocalypse: B-2 Spirit (2 billion dollars of military muscle turned-Decepticon) Would be a bit slow and lumbering due to enormous payload of weapons, but it's pretty much game over when he starts shooting...