US Pledge of Allegiance
The US Pledge of Allegiance has become controversial for a number of reasons. It is of significance due to its widespread use in US classrooms.
Points of contention
The phrase "under God" was officially added to the pledge in the 1950s due to pressure from several pro-Christian groups. The point most often raised is that it implies that the pledger acknowledges the existence of God, which in many circumstances violates the separation of church and state nominally required by the US Constitution. The presence of this phrase is now being used as evidence that "the US is a Christian nation", typically by the same types of groups who campaigned to have it inserted in the first place.
"to 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.
It has also been pointed out that the Pledge makes a number of assertions about the nature of the United States which simply are not true, i.e. that it grants liberty and justice to "all" (presumably at least all US citizens living at home), and that the people who are most insistent on ritualized reciting of the Pledge are many of the same people who have worked the hardest to undermine liberties and deny justice to those without special privileges.
"I pledge allegiance to the Constitution of the United States of America, and to the republic whose law it guides: one nation, indivisible, with liberty and justice for all." (This addresses only the first two points.)