The following is an excerpt from an article on PBS Teachers that I found interesting. Science is often one of the centers we overlook. With a few simple items, we can make our own science centers.

HOW TO INCORPORATE SCIENCE INTO YOUR CLASSROOM

S.A.M.E.'s preschool program focuses on three process skills - observation, classification, and communication. The following science ideas can be taught to preschoolers and can be spiraled as needed.

A good early childhood science program develops the science process skills of observation, classification, and communication. Young children, because of their innate curiosity eagerly embrace all types of science activities. The easiest way to incorporate science into the early childhood classroom is to "find" the science in the activities you are already doing. A lesson about "me" can include making pasta skeletons with the children's pictures as the head. Color mixing, exploring which materials dissolve in water, comparing similarities and difference in objects, and cooking are all science activities.

Set up a science center.
This does not need to be expensive. Large and small magnifiers, prisms, balance scales, mirrors, magnets, color paddles, and a variety of objects to observe and measure are a great way to start. Models and animal puppets are always a hit. Throw in a few theme-related books, puzzles, and writing materials and you're set. Change the materials on a regular basis to keep things interesting.

Teach what you know.
If you like animals or plants, start there. Meal worms make great class pets. They are easy to care for and you can observe their life cycle. Plants come in a variety of sizes, shapes, and textures. They can be observed and measured. Lima bean seeds are easy to plant and grow. Don't forget to include "Jack and the Beanstalk" with this activity. Even teachers without a green thumb can provide plant science activities for their students by bringing in flowers and leaves for children to observe and take apart.

Use your surroundings.
Get pine needles from your Christmas tree vendor, dog fur from your local groomer, pick up pine cones, feathers, leaves, etc. whenever you find them. Ask you local pet shop for snakeskin, feathers, and other animal items. Once the word gets out that you collect these things, people will save them for you.

Be a good observer.
If your students start to do something unusual with an item or use it in a non-standard way, step back and watch. He/she may be making a new discovery and just might teach you a thing or two.

Introduce new items and concepts to the group.
The children need to understand what things are for, and how to use and take care of them. Let them play. Children must have time to freely explore new things before participating in a structured activity.

Answer their questions honestly.
If you don't know an answer, find out. Then, tell the children where you found the answer. Even preschoolers understand looking up information in books, on computer programs, and on the Internet.

The best way to promote science literacy is to expose your students to a variety of books, from preschool level to adult. Just make sure the adult books have lots of pictures. You will need the information in the adult books to answer the children's questions.

A few simple additions to your classroom and curriculum will provide endless opportunities for creative thinking, problem solving, and exploration. You're students will be on their way to becoming "Super Scientists."

Take a look at the full article from PBS Teachers: http://www.pbs.org/teachers/earlychildhood/articles/science.html

How about a tub of sink/float items? This is an activity that you can use over and over and over. Gather items from around the house and keep in a tub that you can pull out either as a planned activitiy or as a time filler.