So far, no one has said anything about ACH or e-checks (direct debits from checking or savings) as a payment method. As was pointed out in this thread, as consumers we love to use credit cards because we get the rewards that businesses ultimately pay for via fees (unless you want to charge a processing fee...which is another can of worms).
Significantly cheaper than paying credit card processing, ACH fees typically run between $0.50 and $1.00 per transaction. Some companies charge a small variable fee (0.10%) for large transactions. All the customer does is give you a bank routing number and their account number.