Montessori Math -- Place Value, Stamp Card Game

I got the Stamp Cards (1 units, 10s, 100s, 1000s for practicing
place value here
http://www.montessorimaterials.org/Math/stampgame1.pdf

-- just print them out on colored paper). My numerals are part
of our curriculum from Right Start math, but you can print them
out from Montessori Matrials here:

http://www.montessorimaterials.org/math1.html)

You can also use these stamp cards to reinforce the fact that
there are never more than 9 units (or nine 10s or nine 100s, etc.). You
throw a bunch of cards out and then trade for a higher place value
card whenever you count 10. So, if you have 23 10s cards you'd trade
10 10-cards for a 100 card, then another 10 10-cards for a 100 card.