Wallpaper it! There are a lot of wallpapers available that would give your ceiling an unique touch. Using bamboo paper with a tropical palm tree border, a faux finish with a classical border, or use a sports themed paper. There are so many paper and borders the possibilities are unlimited.
You could use bamboo which comes in rolls for for ceilings. Cork is possible; it comes it both tiles and rolls. Also, consider tongue and groove wood ceilings.
Clay models, Plaster of Paris, Wooden pannels and Thermocol roofing.Clay models and Plaster of paris can get in any type and in any colour and in any shape according to your wish. Ceiling in woodden pannels will be great in look. You can also use thermocol for ceiling.