US Pledge of Allegiance
The Pledge of Allegiance has become controversial for a number of reasons, largely due to its widespread use in US classrooms.
Under God
The point most often raised is that it implies that the pledger acknowledges the existence of God ("one nation, under God"), which violates the separation of church and state nominally required by the US Constitution.
The Flag
A secondary objection which is gaining popularity is that rather than pledging allegiance "to the flag of the United States", which is essentially an arbitrary and meaningless symbol – thus leaving the pledger's "allegiance" much more prone to manipulation – it would be far better for children (and others) to pledge allegiance to the Constitution of the United States, which would be much more meaningful as well as being specific and more along the lines of the sort of allegiance we as a country would want to inspire in our citizens.