Super thread! I love to see the creative things people come up with to give their interiors a unique touch. One of the things I really miss from TS3 is being able to recolor and decorate the ceiling. I'm one of those people that always looks up, both while building and playing. The only thing I've come up with so far in TS4 is to use shelving (I size it up) to at least line the ceiling on a wall or two:
http://i916.photobucket.com/albums/ad5/SFsimpics/Sims4/Building/BnSPenthouse/dining1_zps6e4a9d08.jpg
Because the shelves have to be against the wall, it's limited, and there are often conflicts with the collision boxes of other objects, but when it can be done, I think it lends a nice touch. If any of you have figured out cool stuff to do with the ceiling, I can't wait to see it!