Largest (voter registration over 100,000)
Constitution Party - Paleoconservatism, paleolibertarianism, Conservative Libertarianism
Green Party - Green politics, eco-socialism, progressivism
Libertarian Party - Libertarianism, laissez-faire
This makes sense- the Greens are far more leftist than the Democrats, yet do not subscribe to socialism (which Americans have a phobia about) or social democracy (which Americans do not know anything about), and the other two parties both cover Americans' minarchist sentiments.