The complexity result of the year goes to The Matching Polytope has Exponential Extension Complexity by Thomas Rothvoss. Last year's paper of the year showed that the Traveling Salesman Problem cannot have a subexponential-size linear program formulation. If one could show that every problem in P has a short polynomial-size LP formulation then we would have a separation of P and NP. Rothvoss' paper shoots down that approach by giving an exponential lower bound for the polynomial-time computable matching problem. This story is reminiscent of the exponential monotone circuit lower bounds first for clique then matching in the 1980's.
If you expand to all of mathematics, one cannot ignore Yitang Zhang's work showing the liminf of the difference between consecutive primes is a constant. Dick and Ken have other great results for the year.
A big year for theoretical computer science. Silvio Micali and Shafi Goldwasser received the ACM Turing Award. The P v NP problem makes a prominent appearance on a major US television series. We are seeing the rise of currencies based on complexity. Large-scale algorithms, cryptography and privacy play center stage in the Snowden revelations on the National Security Agency.
Generally good news on the funding and jobs front in the US. After a year of sequestration and a government shutdown, looks like some stability for science funding now that congress has actually passed a budget. Plenty of theorists got academic jobs last spring and given the number of ads, this year's CS job market should be quite robust as well.
A year for books. Of course my own Golden Ticket as well as Scott Aaronson's Democritus and Tom Cormen's Algorithms Unlocked.
An odd year for the blog in 2013 without a single obituary post. Nevertheless let us remember 4-Colorer Kenneth Appel, Georgia Tech Software Engineering Professor Mary Jean Harrold and Wenqi Huang who led the Institute of Theoretical Computer Sciences at the Huazhong University of Science and Technology. In 2013 we also said goodbye to Alta Vista, Intrade, Google Reader and the CS GRE.
In 2014 we'll have the next installment of My Favorite Ten Complexity Theorems of the Past Decade and the centenaries of George Dantzig and Martin Gardner. Enjoy New Years and keep reading.