This would be a good itinerary for those who would prefer less travel and more relaxing and exploring in one place, although combining some of them in one trip would not be dificult. While island-hopping is a popular activity in Greece, you can have a great experience staying in just one island and perhaps taking small day-trips to the surrounding areas or islands.
I chose these particular islands because my personal experience is that they are large enough, or offer enough variety to warrant an extended stay. I am convinced that there are plenty more worth staying at that I neglected to includ here either because I haven't been there yet, or because I have to keep these web pages a manageable size. All of the destinations in this itinerary contain a bit of everything: beautiful towns and villages, fantastic beaches, enough area to explore with a car, and a few options to explore on day-trips around them.
Kefalonia is a classy island that could keep you busy with it's towns and beaches for more than a week if needed, while Corfu would be impossible to explore in such a short period of time. Kefalonia an island that I would recommend for quiet and family vacations. If you choose Corfu stick to one part of the island. The north is more suited for family vacations, the west packs some of the best beaches, while the south is famous for the nightlife and party beaches. If you choose the North of the island, it would be closer to a day-cruise to Butrint, Albania across the bay for an optional day-trip.
Crete is very large and I would never recommend trying to explore the whole island on one trip. Our family has visited Crete four times in five years and we have yet to explore the whole island. Choose one of the areas (east, center, or west) and you won't regret it. Some of the best beaches of the Crete are located on the west coast, so choose to split your time between Chania and Kissamos for better access to them. From Chania you can go on a day-long hike through the Samaria gorge, and from Kissamos rent a car and drive to Elafonissos and Falassarna beaches. You can reach our current best beach in Greece, Balos via a day-long cruise from Kissamos. If you choose the center of Crete, you can spend the entire time in Heralklion, although splitting your time between the big city and the south (perhaps Matala or Agia marina) would be a better idea. There are plenty of Archaeolgoy around the area to keep you busy every day, and tons of beautiful beaches to relax. For extreme partying, the nearby Hersonissos/Malia seaside resorts could be heavenly for those who prefer tanning while sleeping on the beach by day and partying all night.
Eastern Crete is much more quiet (with the exception of the very busy town of Agios Nikolaos) and it too has some beautiful beaches. If quiet and minimum driving around is your goal, head for the sleepy town of Sitia, or the smaller village of Palekastro that's very close to the beaches of Kouremenos, Chiona, Vai, and Erimoupoli.
Rhodes is also a very large island, but you can easily roam around with a car (not a moped) if you have a week at your disposal. Rhodes town is as beautiful as it is busy. Same goes for the towns beaches, although you might want to drive to some of the more inaccessible beaches around the island. Kos island is a bit smaller, but it has the advantage of being the hub for several day-long trips to Bodrum (Turkey - the ancient Greek port of Halikarnassos), the volcanic island of Nisiros, and the sponge-diving communities of Kalymons. You could acutally split the week between the two islands.
Samos is a large island with beautiful beaches and extensive history. From Samos you'll be well positioned to take short trips to Kusadasi (ancient Ephesus) in Turkey, and the island of the Apocalypse, Patmos.
All of the above islands are far from Athens and it would take a whole day just to get to them if you sail by ferry. You should be able to fly to these islands instead, but tickets sell well ahead of time so planning ahead might serve you well.
A bit closer to Athens and half-a-day's sailing from Pireas, the islands of Naxos, Paros, Santorini, and Mykonos are close enough, and pack enough activities and interest to warrant a whole week's worth of visit to each. They are also close enough to each other (see my "island hopping" itinerary above) to be able to visit a couple of them in one visit. If you are desperate to fill your facebook map with different locations, you could visit all of them in one week, but it would be a break-neck itinerary and you'll only be able to leave Greece having filled your snapshot collection with a hectic travel itinerary.