Books:

Language: An introduction to the study of speech. (link)

Essays and Articles:

The Function of an International Auxiliary Language (link)

External links:

http://stills.nap.edu/readingroom/books/biomems/esapir.html

http://www.bartleby.com/people/Sapir-Ed.html

http://spartan.ac.brocku.ca/~lward/sapir/Documents.html

http://www.yale.edu/linguist/Sapir.html

http://www.mnsu.edu/emuseum/information/biography/pqrst/sapir_edward.html