Every so often I run across someone online asking what they should spend a sizable (but not enormous) amount of money on for their middle or high school math classroom. The dollar amount varies, but it's often in the 500 to 1000 dollar range. That's enough for a nice piece of technology, or a class set of something not-too-pricey, or a number of subscriptions or pieces of software, or lots of small things and supplies, or some combination thereof.
There are many options and many good ideas. I thought that this might be a good forum to collect and upvote ideas on how to spend a chunk of change on a math classroom. Best bang for the buck.
Feel free to offer either a single suggestion that you would purchase or an all-inclusive package for the full sum. In any case, please, give a detailed explanation why you make this specific recommendation, rather than mentioning only some specific product.