Conservative
Constitution Party - Socially conservative, economically libertarian.

Moderate
Reform Party

Liberal
Green Party
Vermont Progressive Party - Progressive party that enjoys modest success on the local (mainly in Burlington) and state levels
Working Families Party - a “satellite” party of the Democrats in New York, where candidates can get a second ballot line.

Libertarian
Libertarian Party - Identifies as fiscally conservative and socially liberal

Other Minor Third Parties
Various other minor parties are given in the list of political parties in the United States.