Went to Ithaki on a day trip this year. Took a ferry from Kefalonia (Sami port) to the island. There's nothing at this port, so make sure you have rented something before you get to the island! (that is, bring a vehicle with you.) The main port is called Vathi and you need to drive about 10 minutes to get there.
Ithaki is a very nice island with some nice beaches. They're a little hard to get to, but if you have transportation, you should be fine. Can't remember the name of this really nice beach, located to the right of Vathi, but the water was very clean. A very peaceful, picturesque, mountainous island...
