We all know that credit cards and similar money cards are haram, so would it be haram to accept donations from such cards?
The credit card itself is a contract between the issuer and client - a merchant has nothing to do with it. As far as the merchant is concerned it is simply a payment made on behalf on the client by the card issuer. There is no interest involved, and whatever percentage the card issuer takes from the merchant for facilitating this transaction counts as a service charge.
There's a hadith where the prophet (salallahu alayhi wa sallam) said:
When the hand changes, the ruling changes.
Based on this hadith, even if someone has haram money -- say they work for a tobacco or alcohol company -- you can accept their money without any issue. (The only exception is stolen property; changing the hand does not absolve it.)
Also, credit cards, from a contract perspective, would be permissible: the credit card company pays you, in lieu of the actual buyer, within a day or two of the sale — no interest involved.
Source: Islamic Finance 101 weekend course; circa 2008.