Here is a bicyclist's account of travels on the Greek island of Corfu in 2000.
With 400 miles of paved roads, Lesvos (Lesbos) is a biker's paradise, as Colleen McGuire discovered on a recent bike journey around the island.
These accounts of travel in Corfu, Rhodes, and Kefalonia should get you rolling: Bike Trip Reports
And one more, through much of mainland Greece: Bicycle Tour Through Greece
For quick sightseeing in Athens, Pame Volta rents bikes every day of the week. They also offer guided cycle tours of the city, and provide suggested route maps if you want to go on your own.
Eurocycle offers an interesting pair of bike trips through both Greece and Turkey, traveling by sailing yacht between islands. They also offer a discount if you book both the trips at the same time. However, be sure to note that the trips reverse direction on alternate weeks, which could affect your flight plans back if you're not careful. Istanbul is long ways from Athens! They're retooling the details on the boat trips for next season - contact them for the final itinerary.
Bicycling offers a special perspective on the beautiful countryside of Greece, and will make many wonderful memories. Enjoy your trip and let me know your experiences.

