Wow, I agree with disneyfaninaz that they have changed the lockers since we were there in May, it has always just dispensed a slip with a code that you have to enter. We have used both cash and credit/debit cards to rent them.
One word of caution: we have twice (but only twice, and we rent a locker every day that we are in the parks) had an issue where the kiosk machine locked up, much like any computer will, and as we had already swiped our card, it deducted the money although we weren't able to get the locker. Both times, we visited City Hall and were quickly refunded the money, and it isn't a big deal to have $10 or so held up on a card, but just fyi. We try to only use cash now, because the freeze problem is apparently more likely when it is processing a card; just for the sake of saving time we use cash when we can.