we took the high speed ferry from Pireas to Naxos. It left Athens at 7:45 am, and got in at 11:45 am or so. It was great. Very comfortable, and quick. We spent the extra 10 euros or so for business class, and I think it was well worth the money.
Renting a motorcycle or scooter is a great way to see the island. Billy's bikes rents all kinds of stuff, and they are very reasonable. Just be careful on the dirt roads, or you'll end up with an unwanted souviner, like I did.
The bus system on Naxos is quite good. Of course there aren´t frequent servies to all the villages. The buses leave from the port in early morning and head for the villages and there are often return buses twice a day, early afternoon and late afternoon.
To the most popular beaches, like Agia Anna, there are frequent bus services all day.
The busride can take some time if you are heading for the inland villages because the bus threads them all. Just enjoy the view.
I can´t remember the prices, think I paid 1-2€ one-way to Filoti, which is in the central of the island.
Naxos is a rather big island, at least compared to most of it´s neighbouring islands so renting a car is a good way of getting around.
The rental prices were dirt cheap in June. We got Daewoo Matiz and paid 25€ for the day.
From Piraeus port, there is at least one daily ferry (6 hr.) and one daily high-speed ferry (4 hr.). At summer the sceduled trips are more.
Information: tel. 210 4593223
Naxos is connected by ferry with Syros, Paros, Ios, Sikinos, Folegandros, Santorini (Thira), Tinos, Mykonos, Amorgos, Koufonissia, Iraklia, Schinousa, Donousa, Crete, Ikaria, Samos, Thesalloniki.
Journey from Piraeus will take 6.5 hours by ferry, while high-speed will take 3.5 hours only. Journey time with ferry from Rafina takes 5 hours while high-speed will take 3 hours only.
I arrived to Naxos in a ferry from Santorini. Naxos is a main maritime hub, so there´s many ferries to surrounding islands.
The closest is Paros, 1 hour away.