There is a beach on one side, but its not very nice, I took a yacht around a bunch of these Islands and I would recommend anyone doing the same, the small less touristy ones are the ones I loved the most and you can find nice little private beaches around the place!. Watch for Jellyfish, some are pretty nasty! about 11 years ago
I know this is a bit late, but I just came back from a 3 day stay in Santorini and here is my opinion: if you want to go to the beach, Perissa was pretty cool. The prettiest beach we went to was Kamari. Oia was beautiful, but touristy and probably more expensive.
We stayed at Stavros Villas in Karterados, and it was the best place I have ever stayed at. Pretty cheap (about 14 euro/person) and we got a really good deal on a rental car (55 euro for 3 days).
I would definitely recommend renting some form of transportation (car, ATV, scooter) because it's a lot more convenient and, quite frankly, cheaper (esp. when split between 4 people).
Hope this helps! almost 11 years ago