Just a word of warning about the Alpha Bank atm in Apollonia which seems to retain more than the occational card, even when you have enough funds in your account!!
Ours disappeared one evening, but when we went to the bank the next day, with passport, for ID purposes to get it back, they said thet we had to get our UK bank to fax them to tell them that it was ok for us to get it back.
They had a least another couple of dozen cards in an envelope so we weren't the only victims. They said that they destroy unclaimed cards at the end of each day!
If you live in the UK you know what it's like phoning you bank from home, so you can imagine the problems we had contacting them and getting them to fax Greece....
We'll be using the Piraeus Bank around the corner by the taxi rank for future withdrawals!!