For anyone using the airport, & particularly for onward flights to the islands here are some useful links.
Who flys where & when, hover on destinations to get airlines covering that route, click on destination for schedules,
http://www.aia.gr/flight_schedule/domestic_en.htm
Athens airport is all one terminal, upstairs for departures, downstairs for arrivals, plan of the airport here, use arrows to move left & right & side tabs for the level,
http://www.aia.gr/flash_files/imap.asp
Please ask any questions that you have on here, including transport options into the city.