Requiescat in pace.
My favourite bit of his writing was On The Impossibility of Drawing a Map of the Empire on a Scale of 1:1:
http://blogs.ubc.ca/clanki/files/2007/04/on-the-impossibility.pdf
which was in turn inspired by Borges' brief conceit, On Exactitude in Science:
https://www.sccs.swarthmore.edu/users/08/bblonder/phys120/docs/borges.pdf
Generally think he had a charming gift for over-extrapolation, and taking premises beyond their logical conclusions in amusing ways, which you can see in all his collected essays.
Another work of his I'm really fond of is The Search for the Perfect Language, which should be read by any mathematician or linguist. It's a terrific popular non-fiction work dwelling on the failed mediaeval project to harmonise all human language in one perfect system of communication.
Of his fiction I only ever read The Name of the Rose, and I don't think it's as good today as I used to think it was when I was younger. I've heard Foucault's Pendulum is very good if you're interested in the occult and the idea of conspiracy.