"Cyclone" tops for goodie bags from Oriental Trading Company.
Spin Tops - Oriental Trading
Playing in the sprinklers with umbrellas. :-)
Sun Sensitive Paper from Steve Spangler Science -- $12.99 for 30 sheets
Sun Sensitive Paper | Steve Spangler Science
Tornado in a bottle experiment
Raindrops and umbrella decoration
Sky Jello: The original recipe is now closed (boo passwords) but here is someone who relisted it. Basically: packages of Berry Blue Jello * 2 cups of whipping cream * 1/4 cup sugar * 2 cups of ice * parfait glasses or any clear containers that you can see through - the key here is to use the ice to quickly set up your jello and you're using ice instead of water. Got that? Cuz I screwed this up the first time I made it.