So many great ones.
Spielberg, Scorcese, Hitchcock, and Kubrick are my definite favorites. Then there's guys like Kurosawa, Leone, Tarantino, Nolan, Anderson (both PT and Wes but much more so the former) that have always made great stuff. Then there's other greats like Wilder, Capra, Welles, Bergman, Hawks, etc. Man, I could spend all day listing my faves. I'll try to think of a more coherent list.