Roman Jakobson & Moris Halle 
Fundamentals of Language [PDF ebook] 

“Jakobson and Halle’s initial statement of the principles of linguistic organization should be made available to all future generations of linguists. It builds a solid foundation for Saussurean thinking about linguisic oppositions and establishes distinctive feature theory as the basis of their formal treatment.”
Prof. Dr. William Labov, University of Pennsylvania, Department of Linguistics