Lewis structure for Nitrogen Dioxide

[Bipolarity]

I am pondering on what the correct Lewis structure(s) for Nitrogen Dioxide (NO2) may be...
I have come up with 7 possible structures, but am unsure which are correct and which are not. I have compiled a small list of notes for your convenience and they are all in this picture.

Which structure(s) are correct and which are incorrect and why?

http://imageshack.us/photo/my-images/202/nitrogendioxide.jpg/

[CrimpJiggler]

Its a resonance structure that is a combination of structures 3 and 4:
http://www.madsci.org/posts/archives/2000-02/951452623.Ch.2.gif
Think about benzene. Its lewis structure isn't actually this:
http://3.bp.blogspot.com/-2xBUfXlfi1Y/Tkf5wkHWFII/AAAAAAAAAF0/A5dSM1zgVJw/s1600/benzene.gif
in reality its Lewis structure is this:
http://www.worldofmolecules.com/solvents/Benz3.png
because the double bonds are constantly changing position.

[Bipolarity]

Its a resonance structure that is a combination of structures 3 and 4:
http://www.madsci.org/posts/archives/2000-02/951452623.Ch.2.gif
Think about benzene. Its lewis structure isn't actually this:
http://3.bp.blogspot.com/-2xBUfXlfi1Y/Tkf5wkHWFII/AAAAAAAAAF0/A5dSM1zgVJw/s1600/benzene.gif
in reality its Lewis structure is this:
http://www.worldofmolecules.com/solvents/Benz3.png
because the double bonds are constantly changing position.

But shouldn't the electrons be placed on the more electronegative atom, i.e. oxygen, so that nitrogen gets the lone pair, giving it Lewis structures 1 and 2?

[CrimpJiggler]

Good point. In this video:
https://www.youtube.com/watch?feature=player_embedded&v=q37GtTpTAzg#!
the guy draws is like that.

[That Neuron]

It is chemical resonance, as CrimpJiggler said, but its not so much that the electrons are in constant fluctuation, but rather the odd electrons that could be bonded or non-bonded are involved in a sort of delocalized electron orbital that surrounds the entire molecule, apparently the delocalization of the electrons actually lowers their potential, making the resonant molecule more stable than either standard lewis formation.

[DrDu]

In fact, you any valence structure which is compartible with none of the orbitals being filled by more than two electrons and a total of 23 electrons is valid and will contribute to some extent to the true wavefunction of the molecule. The relative importance of the structures depends not only on the molecule itself but also on the orbital basis considered (i.e. s and p type or hybrids, orthogonalized or not).
Nevertheless the two structures shown in the video will probably be most important, at least for a qualitative description of the molecule.