When I read the title of this thread, the first thing i thought of was Reki’s room in Haibane Renmei. Have you seen it?
All right, I’ll try to be more serious, though I don’t seem to be a generator of good ideas. 
But I think it could be rather dreamy to have there some photos of different people or short scriptures, covered with distorting or matted glass.
An animal could really be placed there… Like a hamster in a cage. It doesn’t sound out of ordinary, but sometimes they look so surreal… If you have no time to feed it, you can grow strange flowers in this room. And you have no time to water them… 
I don’t know.
Some scriptures in a non-existing language could be cool, too.