Don't be afraid to go wild and paint the ceiling! My granddaughter wanted her room at our house painted hot pink and lime green to match the colors in the curtains, sheets and bedspread. So we painted two walls hot pink and two walls lime green. Then I nearly broke my neck, painting flowers on the ceiling to match the linens and liven up the space.
After all it is only paint and can be painted over when it is time to change the decoration.
On a couple of the corners I painted the flower petals down onto the wall below, just for fun. Those are some of the paintings she did in art class when she was ten.
Don't worry about trying to make all of the flowers or whatever match exactly. It is way more interesting if you do a variety. I spaced them differently and made small and large ones all over the entire ceiling. I painted different color centers in the flowers to bring in the other colors in the curtains and bed linens. Since I was free handing it worked great. Except for my neck.
You can see the curtains in a couple of the photos above. This is the bed spread and the sheets match the curtains. It is certainly bright and wild in this small bedroom.
I found this neat photo frame that had similar "flower" shapes, around the word FAMILY, to add to the room. This photo makes the walls look more gold, but it is really lime green. She and her friends loved it. We often forget the ceiling when adding flare to our decorating plans. Another thing I have seen is the vinyl wall clings for decorating children's rooms. There are also vinyl cling sayings usually used over doorways, etc. Either of these would be great on the ceiling!