The two most important amendments in the Bill of Rights
To many, the First Amendment is the most important, as it (supposedly) prevents the government from infringing upon the rights of the people to freedom of speech, religion, and assembly, and prevents the government from making any laws "respecting an establishment of religion".
Other people believe the Second Amendment is most important, because a government which can disarm us leaves us no ability to protect ourselves, or the Fourth Amendment (no unreasonable searches or seizures), or the Fifth Amendment (due process guarantee, no requirement to testify against oneself).
However, I personally believe that the Ninth and Tenth Amendments are truly the most important and most far reaching of all of them:
The enumeration in the Constitution, of certain rights, shall not be construed to deny or disparage others retained by the people.
The powers not delegated to the United States by the Constitution, nor prohibited by it to the states, are reserved to the states respectively, or to the people.
I will post more at length when I have more time, but these two very short statements say, quite clearly:
Amendment IX: The people have far more rights than those listed in the Constitution. Just because a right is not listed in the Constitution or in an Amendment doesn't mean that it's not a right. So all those who would say that some particular thing (e.g., privacy) is not a Constitutionally protected right, are dead wrong. The people have many more rights (perhaps infinitely more) than are written down. It's up to the legislative and judicial branches of the government to decide what may or may not be a right at any given time.
Amendment X: The US Government may only do what the Constitution gives it the power to do. Congress may not make laws which fall outside the bounds of the powers given to it in Article I of the Constitution; the President is constrained to only those powers listed in Article II (very limited powers, actually); and the Judiciary is likewise limited by Article III. The states may make laws outside these restrictions, but the Federal government may not.
It's a shame that so few people really understand how little power the government was given by the founders, and how much power it has simply grabbed for itself, some would say illegally.
People also seldom realize that our rights are not granted individually by the Constitution and Bill of Rights, but rather the Ninth Amendment explicitly says that we have far more rights than could ever been written into any Amendments.
The people do have the power. When will they realize it?