Great for stacking, sorting, counting, fine-motor development, etc...

Explore the concepts of weight and balance while practicing taking turns (and having fun!)...

I like that this weight box has a self-check option with the colored dots. It can be used as a memory or matching game with the colors, a stacking challenge, or simply a chance to explore and compare the different weights. If you have a small kitchen scale or sturdy balancing scale, you could also give your child a chance to explore this tool using this set.

These are great for creative play as well as for making specific shapes, letters, numbers, etc.

There is also a level one set called Playful Pals by the same author (and higher levels, if your pre-k child is ready for them)...

There are a few books in this series that help build fine-motor skills and dexterity through activities such as folding, coloring, tracing, etc.

Just about any variety of arts and crafts supplies will do the trick!

Kids this age learn the most from playing! Old clothes/costumes, sheets for forts, large cardboard boxes, etc., are all great additions to dramatic play areas. I like tents like this (which usually run around $20) since they can pop up and then be put away easily.