THINGS I BELIEVE EVERYONE SHOULD READ
The list below contains a few titles (papers, books, and manuscripts) in no particular order that I honestly believe every single person that does mathematics would benefit from reading.
I tried to get at least one text that exemplifies the different aspects of my research interests (all written better than I could have done it), and other subjects.
J. Matoušek, Using the Borsuk-Ulam Theorem
The title is self-explanatory, but it is the best refernce I can give for people that are interested in the topological aspects of discrete geometry. Matoušek has many other books, all the ones I've read I would recommned, but this one stands out as my favorite.
D. Lubell, A short proof of Sperner's lemma
Journal of Combinatorial Theory, (1966) 1.2 p299.
My favorite one-page paper.