If you want to write on balloons and have it stay when the balloon is inflated or deflated you might try "balloon markers" by Qualatex. Other than that I don't know.
Some people like using the Expo Dry Erase 2 markers. Supposedly they don't smear the way Sharpies do when the balloon is deflated. From what I have been told, they have to be Expo Dry Erase "2"