Federalism - United States of America - Power is shared between a central government and local governments. Powers are usually separated by the constitution.
Confederation - No true confederation in existence (EU has some characteristics of a confederation) - A group of sovereign countries who have united to deal with situations such as defense, foreign affairs, and a common currency.
Unitary - United Kingdom - The country is ruled by a single government. Local government may exist, but only because the central government allows them to.