iCivics - Excellent civics resources, founded by U.S. Supreme Court Justice Sandra Day O'Connor.  Dig into it... there are games, study guides, interactive websites, and much more.

IXL Learn Civics - An awesome learning/practice website filled with short quizzes, sorted by topic and grade level.  Check this one out to study for assessments!

Constitution Center Games - The National Constitution Center hosts a series of online games that will help you practice your understanding of the Constitution and the Bill of Rights, as well as your knowledge of America's founding.

Crash Course US History: The Constitution - Crash Course is a YouTube series of videos that presents a lot of information about a lot of stuff, and does it pretty fast with entertaining graphics.  This episode is all about the creation of the Constitution, and why not all of it works as well as we thought it would.

Ben's Guide to the U.S. Government - A kid-friendly website filled with information, games, and activities - hosted by American legend Benjamin Franklin - that can help you learn all about the government and Constitution of the United States.

Financial Soccer - A soccer-themed game for learning about some basic economics and financial decision making.

Econ Essentials - A website with several interactive learning modules all about economics and personal finance.