In the Scifi category, I'd recommend "The Languages of Pao" [1] by Jack Vance, which is inspired by the Sapir-Whorf hypothesis [2]. I've re-read it five times now, which means this book deserves the space it occupies in my bookshelf. Books that are only worth to be read once, you might as well throw away.

[1] http://en.wikipedia.org/wiki/The_Languages_of_Pao [2] http://en.wikipedia.org/wiki/Sapir%E2%80%93Whorf_hypothesis