What are the most important papers in physics? Recently I got the book "On the Shoulders of Giant" from Stephen Hawkings. It consists of more than 1000 pages of classical publications in physics. However 900 pages are given to the work of Copernicus, Galilei and Newton and 100 pages are given to the papers of Einstein. Therefore I think this books gives a wrong impression about what is really important for our knowledge in physics today. 
If you could fill a book with the most important papers relevant for our knowledge in physics today, which ones would you select?    
 A: The two papers of fundamentals of Density Functional Theory.

*

*P. Hohenberg and W. Kohn. Phys. Rev. 136, B864–B871 (1964)


*W. Kohn and L. J. Sham. Phys. Rev. 140, A1133–A1138 (1965)
The Kohn-Sham paper have 10,575 citations and the Hohenberg-Kohn have 8,714 citations. These papers are importants for Condensed Matter Physics, Atomic and Molecular Physics, Quantum Chemistry and Nanoscience in general. It is a prime example of interdisciplinarity.
A: I know it's been mentioned already here, but:
A Model of Leptons
is worth every bit of its (almost) 4 pages.
Recently, the one that changed everything in theoretical physics is:
The Large N limit of superconformal field theories and supergravity
perhaps it already deserves to be in this listing.
A: E. Wigner, "On Unitary Representations of the Inhomogeneous Lorentz Group"
Because of the apocryphal story of how it got published.
Edit: It was originally rejected by one of the leading physics journals as not being of general interest. Then Wigner mentioned it to von Neumann (his classmate from school back in Hungary). J. von Neumann told Wigner to send it to the Annals of Math., where von Neumann was the chief editor. It was immediately accepted there! Years later, Wigner received a leter from the AMS, saying that after a survey his paper had been found to be one of the most influential papers.  
A: The birth of computational physics:
N. Metropolis, A.W. Rosenbluth, M.N. Rosenbluth, A.H. Teller, and E. Teller (1953). "Equation of State Calculations by Fast Computing Machines". Journal of Chemical Physics 21 (6): 1087–1092. doi:10.1063/1.1699114.
A: In the field of statistical physics there is nothing more famous than Onsager's solution for the Ising ferromagnet on a square lattice.
Crystal Statistics. I. A Two-Dimensional Model with an Order-Disorder Transition
The paper itself isn't that important nowadays because there are both better solutions and better pedagogical approaches to the problem. Nevertheless, historically it was the first full solution of a non-trivial physical system which exhibits phase transitions.
A: The number of citations a paper receives is a good indicator of its importance.
Top Cited Articles of All Time (2010 edition) can be found at:
http://www.slac.stanford.edu/spires/topcites/2010/alltime.shtml
1.37791
Review of Particle Physics
By Particle Data Group (Claude Amsler et al.). 
Citations are counted for all versions of the RPP, most recent version is: 
Published in:Phys.Lett.B667:1-1340,2008 
[3679 Total citations in HEP] 
[37799 Total Citations to all copies of RPP in HEP]
2.7328
A Model of Leptons
By Steven Weinberg (MIT, LNS). 
Published in:Phys.Rev.Lett.19:1264-1266,1967 
[7328 Total citations in HEP] 
3.7135
The Large N limit of superconformal field theories and supergravity
By Juan Martin Maldacena (Harvard U.). 
Published in:Adv.Theor.Math.Phys.2:231-252,1998, Int.J.Theor.Phys.38:1113-1133,1999 (arXiv: hep-th/9711200) 
[7192 Total citations in HEP]
A: These days, the most important papers are generally the ones that get the most citations.
Papers' citations are listed at Spires (or Inspires) at Inspires.
Simply look up an author then click on his/her name and go to citations. They rank the papers by means of citations from "unknown papers" to "renowned papers". It is hard to rank the older guard of physicists this way.
Stephen Hawking collected what he regards as important original papers of the greats(I note that you have that) in "On the Shoulders of Giants" and a similar book of original math papers And God Created the Integers
As an aside, Sidney Coleman said that if he had seen farther than others it was because he was standing behind the shoulders of dwarfs....:)
Oh, I see you have On the Shoulders,...well others are George Johnson's , The Ten Most Beautiful Experiments, or The Great Equations, by Robert Crease.
