Most of the timetables you will find do not apply for the summer months to come as they might increase the density of routes when they see fit. You could try this site: http://www.airtickets.gr/ferries?gclid=COq7uNDDlsQCFagfwwod9DkAPw which is in Greek (couldn't find English for the ferries schedule). e.g. on the 4th June there is one afternoon route from Santorini to Folegandros, the trip takes around 45minutes and the fare is 44€ which is a total ripoff by the way! You can right down the name of the island in English and it will appear in Greek underneath just to give you an idea.

Santorini: Great scenery, many tourists, nice villages, great strong local wine. Mykonos: As some single males in mid 40s say, "In Mykonos and Ukraine you travel alone" (a lot of beautiful women). Again full of tourists and celebrities but some nice quite beaches also. Folegandros: Nice scenery with hotels built on top of rocks/cliffs with a great ocean view. Paros: Popular destination among Greeks. Milos: Same as Paros with a great beach called Sarakiniko That is looking like the Lunar surface. Ios: Popular destination for UNI students and young people of age who like to party. (and all that comes with it) Most of them stay in camping sites with tents. Naxos: big island few nice beaches and good local food and dairy products.

Now at the time you will come to Greece even Ios will not be full of people. Peak months are considered July-mid August.

sources: Been in Santorini in the summer, Milos and Naxos in the winter (work related visit) and know that Folegandros is secluded by my brother who has been there a couple of times.