I've purchased stools from two different sources for two different churches.

My favorite ones are the ones from Wal-Mart mentioned above by Heather.

We also bought the wood topped ones for our art room and painted them in primary colors. One of our artists then painted pairs of animals on each one - our art room is called "Noah's Art."

In our computer lab we use another Wal-Mart stool with a black vinyl padded seat.

I find the lower stools generally work better than higher ones, but that depends on your table size.