I often assign pages 1-49 of Orientalism, and also like to teach this article:
Said, Edward. 1989. “Representing the Colonized: Anthropology’s Interlocutors,” Critical Inquiry 15(2): 205-225.
Depending on what you're doing, I might use excerpts from his other works, rather than several from Orientalism. Culture and Imperialism is also worth taking a look at although I haven't taught anything from it myself.
Also, see Keith Hart's suggestion in this discussion for a BBC documentary program to use alongside the teaching of Edward Said's work.