If price is a consideration (of course with the exchange rate of the U.S. dollar that goes without saying), Blue Star Ferries is currently offering a good deal on tickets.
From Athens...only 10 Euros to the Cyclades Islands. and 20 Euros to the Dodecanese Islands.
Additionally children 4 - 10 years get a 50% discount, and children up to 4 years get a 100% discount.
http://www.bluestarferries.com
Click on "offers"