How about a falling leaves globe? Try out this Fall Leaf "Snow Globes" project via Frugal Fun 4 Boys.will coat stick so water won't turn brown.
Connect art, math, and science with this project idea - creating trees with warm and cool colors
This is beautiful carved wood. But I think it might work with leaves mod-podged to a balloon, balloon then popped and removed. I think it would be gorgeous as centerpieces--if it worked.