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)...

This set nicely combines block play (spatial awareness, hand-eye coordination, etc.) with elements of pretend play. You can find other sets like it in different themes (castle, town, vehicles, and so forth) by the same company.

There are a number of great puzzles from this company and others like it - again, I'm listing just a couple that I've personally used, but there are more to be found off these product listings.

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.