I can't find the link now, but somewhere there is a site for learning how to do algebra using legos!
I second (third?) all the previous ideas. Beans, buttons, blocks--all great for math. I like to play dice games, too, just making up rules. For instance, roll four dice then try to combine the numbers using each of the mathematical signs (+, -, x, /) to come up with the highest or lowest or whatever number you want. Whoever can get closest to whatever you're going for wins.
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