Many airports in Greece have a Greek National Tourist Organization (GNTO) desk. When they're open, they are always good for a free map of Greece, but they may have other treasures behind the counter. You can also write to the GNTO and request that materials are sent to you, but allow plenty of time in advance of your trip.
Here are some of my favorites.
Ask for this handy, detailed map of Greece which also shows Athens. Traveling with others? Get one for everybody - it's a rule of travel that only one of you will have it handy at any given moment.
Excellent guide to Athens and Attica, fully illustrated, printed on glossy paper. Includes a detailed map of major sights in Athens, though the street names are in very small print. It includes all the highlights in a light, easy-to-carry volume. You can also request it be sent to you by writing to printed@gnto.com; be sure you include your name and full mailing address, including country name.
Entertaining booklet on the Cycladic islands, which include Santorini and Mykonos.
Can't wait? While these downloadable maps won't be as convenient, they're great for pre-trip planning and reference. Choose from a wide variety of road maps, maps of mountain paths, and other maps of Greece. Note: these are in zip files; you may need a zip file program to open them.
This is my favorite - a detailed, fascinating guide to walking through Athens, visiting various historical sites, both ancient and modern. Handy size, very readable. Unfortunately, it's not available on-line nad must be ordered in its print form, or asked for at the counter.
6. Bus 400 Schedule
This simple booklet can save you from spending too much on a day-long coach tour of Athens. The so-called "tourist bus" offers easy transportation between many of the most famous sites, and it costs just 5 Euro for a day's travel. Bus personnel will be happy to give you information about various sites to visit. Since this bus competes with the "big" tour buses which give hotels commissions on bookings, schedules can be surprisingly hard to find elsewhere. Grab one before you leave the airport.