British Council Morocco
When I was in Morocco, the British Council Bookstore was one of the few sources for books in English, particularly books for students of English. The books were good, but not cheap, and I used to lend them out to my students for a few days at a time. I wonder how much has changed.
Bill, you will have to visit Cafe des Livres next time you are in Marrakech. It's a great place to get English books, too.