My three year old is beginning to show more of an interest in school these days, so I am working on getting his little course of study together.
Here are some science resources that I have come across for preschoolers:
Very simple science experiments to do with your preschooler
105 Preschool Science experiments
More simple ideas
Anytime activities and activites arranged by season.
Arranged by categories such as physics, weather, biology, nature, astronomy, hydrology, and experiments.
Preschool Science Lesson Plans, ages 3-6