I have this issue and I am reminded of it every day that I wake up. My ceiling is bare. It's not flat - I have this decorative trey ceiling complete with trim. But it is still fairly boring and it needs help.

All ceilings should have something interesting to look at. Whether it is an inspiring color or some detail that you like. I think that this is important, especially in hospitals - where there are so many people who stare at the ceilings all day. It could be a surface for inspiration. I mean - imagine if you could stare at the work of Chagall or Michelangelo? That might just make a few people feel better while they're stuck in a hospital bed.

Anyway - I think I've found a stencil company that I'll use. Visit them here: Modello Designs.
They have beautiful designs, and you can even design your own stencil from your own artwork. And that's all I needed to see to make my decision.

Of course there are other ways to create something interesting for your ceiling: