Four excellent bookstores I miss from when I lived in Los Angeles:
Hennessey + Ingalls a wonderful Architectural and Art bookstore on the Santa Monica Promenade; Opamp Technical Books – killer technical book selection located in dingy and wonderful Hollywood; Book Soup – nice general interest bookstore on Sunset Boulevard; Midnight Special Bookstore – cool indie bookstore, great selection, on the Santa Monica Promenade.

Some of these stores also allow you to buy online.

(Forgive me this nostalgic moment)