Suggested items: Rulers and other geometric tools, an Abacus, playing cards, magnetic numbers with metal trays, clocks, pegs and pegboards, geoboards, balance scale, tactile numbers, dice, egg timer, lotto games, cash register with play money, tape measure, unifix cubes, dominos, counting cubes, thermometers,......

Stopwatches are fun too!

If you can't buy "Numbered Stepping Stones," they can be made quite easily by printing numbers on thick cardboard squares (another resource from your local photography shop).
 

Pattern Cards: If you have a set of stringing beads in your classroom, extend the activity by making pattern cards which show children the order in which to string the beads.  These can be created by simply drawing around the beads then coloring them in.  For example, one card might have two red beads, followed by 3 yellow beads, followed by 2 red beads, by 3 yellow, etc.  Children string beads following the patterns.

Number Match: Draw around large number stencils (1-10) on a large piece of white posterboard, leaving only their outlines.  Draw around the stencils again on various colors of posterboard but cut them out.  Children match the loose numbers to the ones on the posterboard chart.  For younger children, outline the numbers on the chart using markers that are the same colors as the corresponding matches.  To increase the difficulty, use a black marker to outline the numbers on the chart and cut all the corresponding loose numbers from black posterboard.

Heavy/Light: Fill 3-5 opaque containers with different amounts of sand.  Children line up the containers in order from lightest to heaviest in weight.  Make sure the amounts of sand are obviously different or the children won't be able to tell which is heavier.

Index Card Number Puzzles: Cut large index cards in half creating 2-piece puzzles.  For each two piece puzzle, print a number on one half and place that number of stickers on the other half.  For younger children, make the cut-lines different for each puzzle (straight, curved, jagged, etc).  This way, those who aren't yet proficient in counting can still be successful at playing the game by matching the cut-lines.

Cube Pattern Cards:  If you have a set of those small colored wooden counting cubes, make a set of patterning cards to put out with them: Simply draw around each cube then color it in.  Children can stack corresponding cubes atop the cards or create patterns beside the cards (instead of on top of them) using the same cubes as indicated on the cards.
 
*In the past, when cramped for space, I'd alternate weekly between a math and science center.
**I personally consider the classroom Water Table to be an extension of the Math, Science, and Fine Motor Centers.
 

Suggested basic items: Water table area, magnets, magnifying glasses, thermometer, telescope, microscope, compass, flashlights, prisms, kaleidoscope,.....

To add nature to your science table: Plants for watering, leaves, sticks, bark samples, stones, bird feathers, snake skin, bird nest, bugs, sea shells, weeds,......
I live in Florida, the land of Palm trees, but I'm from up north in Ohio.  One year, in the fall, my parents sent me a big box of real leaves from our northern trees for my classroom.  They carefully placed each leaf (large and small ones) in slightly damp paper towels and baggies, so they arrived fresh.  Believe it or not, I placed them in my Water Table (no water) for children to use as they saw fit for the whole month of October.  My Florida kids loved them.  It was fantastic!

Although I haven't done it, I've always wanted to have a pet cat in the classroom that would be a part of the children's everyday life.  They would name and care for him/her.  The kitty would grow along with the children.  I guess my concern has always been that it might be too stressful for the kitty!  >^..^<
 
And, I don't want to forget to mention having a COMPUTER CENTER, one that unfortunately, I've had only a little experience with since computers have not been in most preschool classrooms where I've worked.  It's great to know things are changing!