I like the original paper by Shannon "A Mathematical Theory of Communication" (http://people.math.harvard.edu/~ctm/home/text/others/shannon/entropy/entropy.pdf

I like the original paper by Shannon "A Mathematical Theory of Communication" (http://people.math.harvard.edu/~ctm/home/text/others/shannon/entropy/entropy.pdf http://people.math.harvard.edu/~ctm/home/text/others/shannon...) a lot. It is quite readable and also probably the most important paper in the field of information theory.