I've been to some houses where the shutters had no gaps and they fit the window frame so well that virtually no light made it in, even during the day. It was surreal waking up in the morning, thinking it was still night time, then checking the clock only to see it was 8AM. A great feature to add to a house if you ask me.
Alternatively, IKEA makes a great little set of curtain tracks (VIDGA) you can attach to your ceiling to get full floor-to-ceiling blackout in a room, similar to many hotel rooms.
