Stephen A. Cook, The complexity of theorem-proving procedures, Proceedings of the third annual ACM symposium on Theory of computing, p.151-158, May 03-05, 1971, Shaker Heights, Ohio, United States

Karp, R. 1972. Reducibility among combinatorial problems. In Complexity of Computer Computations, R. E. Miller and J. W. Thatcher, ed. Advances in Computing Research. Plenum Press, New York, pp. 85-103.

John von Neumann. First draft of a report on the EDVAC. Contract No. W-670-ORD-492, Moore School of Electrical Engineering, University of Pennsylvania, Philadelphia. Reprinted (in part) in Randell, Brian. 1982. Origins of Digital Computers: Selected Papers, Springer-Verlag, Berlin Heidelberg, June 1945.

This one is not really a classic but it is still important with regards to Quantum Computing.

David P.DiVincenzo,The Physical Implementation of Quantum Computation,IBM T.J. Watson Research Center,Yorktown Heights, NY 10598 USA