Costco.com accepts the following forms of payment:
However, as of 2009, Costco does accept Food Stamps at most or all locations.
According to other news, in their Seattle, WA warehouse stores (their headquarters are just down I-90 in Issaquah) they accept debit/ATM cards (or have an ATM machine) EBT cards (food stamps) as well.
In 2009 Costco did begin accepting Food Stamps at all stores.
If you have any doubt, first call the store by getting the phone number by the store locator and speaking to the manager. http://www.costco.com/warehouse/warehousedetails.aspx
Costco began accepting food stamps in 2009.