Local recycling centers typically accept cardboard and other paper products, and many municipal recycling services allow people to place cardboard in bins. Another option to consider is donating boxes to help people who are moving.
Most cardboard is recyclable, but the low cost of corrugated cardboard means that recycling centers generally don't pay for it, the way they often do for aluminum. Not all cardboard is recyclable. Wet cardboard, for example, can clog sorting machines, and cardboard that's been contaminated with oil or other food products can't be recycled. Be sure to flatten cardboard before bringing it to a recycling center to make it easier to feed through machines.