These interactive maps from the Economist provide an interesting comparison between different countries and US states.

Using the criteria of GDP (Gross Domestic Product), the economy of California is approximately the size of Italy, Texas the size of Russia, Florida the size of the Netherlands, and Alabama the size of Nigeria.

Using the criteria of Population, California is approximately the size of Poland, Washington  the size of Lebanon, Arizona the size of Libya, and Minnesota the size of Finland, to name a few.