Freedom of Movement

This is a right which asserts that a citizen of a state in which that citizen is present has the liberty to travel, reside in, and/or work in any part of a country where one pleases within the limits of respect for the liberty and rights of others, and to leave that Country and return at any time. Some immigrants' rights advocates assert that human beings have a fundamental human right to mobility not only within a country but between nations.
It's probably the only thing I agree with Libertarians.  People should be able to live wherever they want.
Never heard of this right?  You seem to talk a lot about rights, but somehow you missed this one?  I think somebody may have mentioned this right without understanding it, but that would be typical for that person as he doesn't really understand as much as he thinks he does.
Yes, it's actually in the US Constitution, but I could guess that you wouldn't know it since you are too fixated on the misinterpreted portion called the Second Amendment.
This right is found in the Privileges and Immunities Clause of the United States Constitution which states, "The Citizens of each State shall be entitled to all Privileges and Immunities of Citizens in the several States." As far back as the circuit court ruling in Corfield v. Coryell, 6 Fed. Cas. 546 (1823), the Supreme Court recognized freedom of movement as a fundamental Constitutional right. In Paul v. Virginia, 75 U.S. 168 (1869), the Court defined freedom of movement as "right of free ingress into other States, and egress from them."
At one time, passports were not obligatory, but they have become part of the modern world since the 14-18 (First World) War.  I think they are kind of fun, but I miss the old blue British Passports which have been replaced by the standardised EU passports.
The Universal Declaration of Human Rights (AKA the International Bill of Rights) mentions this right in a couple of sections:
Article 13 of the Universal Declaration of Human Rights reads:

(1) Everyone has the right to freedom of movement and residence within the borders of each State.

(2) Everyone has the right to leave any country, including his own, and to return to his country.

Article 12 of the International Covenant on Civil and Political Rights incorporates this right into treaty law:

(1) Everyone lawfully within the territory of a State shall, within that territory, have the right to liberty of movement and freedom to choose his residence.

(2) Everyone shall be free to leave any country, including his own.

(3) The above-mentioned rights shall not be subject to any restrictions except those provided by law, are necessary to protect national security, public order (ordre publique), public health or morals or the rights and freedoms of others, and are consistent with the other rights recognized in the present Covenant.

(4) No one shall be arbitrarily deprived of the right to enter his own country.

Technically, Palestinian refugees, especially those who were born in the country now called Israel are technically entitled to move back to their homeland under this charter--so, that means that the State of Israel violates the human rights of Palestinians to return to their homeland.
Of course, the Universal Declaration of Human Rights is one of those documents promulgated by the Evil United Nations (which pays at least one blogger here's salary).
Free movement of workers is a fundamental principle of the Treaty of Rome, which established the European Union.  It is found in Article 45 of that Treaty which states:

1. Freedom of movement for workers shall be secured within the Community.
2. Such freedom of movement shall entail the abolition of any discrimination based on nationality between workers of the Member States as regards employment, remuneration and other conditions of work and employment.
3. It shall entail the right, subject to limitations justified on grounds of public policy, public security or public health:

   (a) to accept offers of employment actually made;

   (b) to move freely within the territory of Member States for this purpose;

   (c) to stay in a Member State for the purpose of employment in accordance with the provisions governing the employment of nationals of that State laid down by law, regulation or administrative action;

   (d) to remain in the territory of a Member State after having been employed in that State, subject to conditions which shall be embodied in implementing regulations to be drawn up by the Commission.

4. The provisions of this article shall not apply to employment in the public service.

 The European Union has adopted a Directive on the right of citizens of the Union to move and reside freely within the Member States to implement this section of the treaty[1], which is a source of great consternation to people in countries such as Britain who find they now have people wanting to move to their country from the former Eastern Bloc nations which are part of the EU (e.g., Poland and Romania).
The right of free movement has actually been around for some time (subject to people's ability to pay to move).  Scholars have attempted to base a universal "right to move" on several philosophical grounds, including the idea of a common ownership of the earth, a natural right of movement existing prior to the advent of nation states, an ethics of cosmopolitanism, and utilitarian notions of the benefits of immigration to both receiving countries and immigrants.
There are a few reasons that I mention this right.  a couple are personal, as one of my passports is up for renewal (I value the right of freedom of movement above all others due to the next reason).  I also value the ability to get out of Dodge should whatever place I reside happen to become unlivable: in the case of the US due to pseudopatriots who would plunge their nation into war.  That's actually quite a good reason in that people in the US are idiots who, while talking peace, are all too willing to plunge their nation into a war.  Fortunately for them, they have been able to stay out of the way for all but a few of their wars.
Unfortunately, they tend to forget the ravages that their nation has suffered because of war.
Anyway, unlike the fictitious or misinterpreted rights I see mentioned here (e.g. "gun rights"), this one is one with serious historic, legal, and ethical bases.
That said, there is one thing that General Patton said which I can agree with and that is:

The object of war is not to die for your country but to make the other bastard die for his.

 Trust me, if you want to start a war, there will be enough people who will be willing to make sure you die for your country.
The object of war is not to die for your country but to make the other bastard die for his.
Read more at http://www.brainyquote.com/quotes/quotes/g/georgespa102496.html#MlqijqW63SW5eB2c.99
I am a citizen of the world.  I can travel and live where I want.
Thinking about this after I wrote it, that was sort of a flip conclusion, but I do write about a lot of complicated topic and try to simplify them.  But, this is one with a lot of ramifications: especially for modern US society.  For example, the way that people dislike Hispanic immigration while neglecting that most of the Southwestern United States (at least Texas, New Mexico, Arizona, and California) were part of Mexico prior to their conquest by war.  Like the Palestinians, those people have a right to access to their homelands and travel to visit their families.  Similarly, the Native Americans have a right to their homeland under this principle.
As I said, the US has a belligerent streak which has caused it more problems than they realize.  And will continue to cause it problems as long as it is not addressed.
[1]   European Parliament and Council Directive 2004/38/EC of 29 April 2004 on the right of citizens of the Union and their family members to move and reside freely within the territory of the Member States