The opening line to The Gunslinger made me want to keep reading. "The man in black fled across the desert, and the gunslinger followed. " The sentence is so simple, yet it raises so many questions that you need to keep reading in order to understand. Who is the man in black? Who is the gunslinger? Why is one following the other? (I will admit that my patience wore thin for a while later on reading, which I still am, but I'm still interested enough in the story to continue.)

Same thing for the opening text of The Night Circus. "The circus arrives without warning. No announcements precede it. It is simply there, when yesterday it was not." I fall all over this kind of stuff. Mystery intrigues me. Forcing me to ask questions is my favorite kind of introduction to a story.

I'll post more when I've had some time to think on others!