I believe the ferry time between Athens (it is actually nearby Piraeus) and Santorini is about 9 hours. edited to add: I think there are also faster ferries, and hydrofoils as well. And you can fly.

Ferries

Yes, I think your trip is a bit aggressive, because of travel time between destinations. Flying can facilitate the journey, but sometimes that can be problematic as well.
If it were up to me, I would probably skip Paris/Cannes, which are quite far apart anyway (but doable. It’s all doable, just kinda crazy and rushed.)
I’ve never been to Mykonos, though I hope to some day. I am sure that there is plenty of the blue/white thing going on. And you
There is lots of blue-and-white on Santorini, which is one of the most breathtakingly beautiful places I’ve ever seen.
I think your budget is fine.
Hostels/hotels can be addressed in the hostels forum.

 
That’s a pretty rushed schedule.  Personally, I wouldn’t bother going to Paris or Rome for less than 5 days.  They’re such big cities and they take time to properly explore and get oriented.
 
I’d keep Cannes, but drop Venice.  I’d also spend the time on the Greek Islands rather than Athens.  You’re probably best looking for budget flights between cities if you’re strapped for time, although train connections run thru most of the cities you want

I can tell you about Greece.  I agree with what heavydrinker said about Athens.  I went to Greece in late May and spent just half a day there, and felt like that was enough (maybe a few more hours would have been good).  Talking to people about Greece before I went, most people said “oh yeah one day in Athens is all you need.”  The Acropolis is a must-see.
 
It is easy to travel between Athens and the islands and then between the islands because there are lots of boat agencies around.  In Athens, you’d probably have to go to the port to find them, but you could also just ask the hotel owners/workers in Athens where to go.  Go to the port ahead of time though to buy your tickets, because if you buy them immediately before there might not be the cheap seats left (that’s what happened to us).  On the islands, the boat agencies are everywhere.
 
There are not really hostels on the islands, but there are really nice cheap hotels.  If you’re booking on the spot, bargain with them.
 
I would really, really recommend not just going to Mykonos and Santorini.  I didn’t go to Santorini, but I went to Mykonos for one day.  It definitely has those nice blue and white buildings.  The streets are pretty and it’s a good place to party, and it’s very cosmopolitan.  My problem with it though was that after walking around in the town for a while, things started to look the same (just lots of clothing and jewelry shops).  Travel between the islands is really easy, so it wouldn’t be hard to go to another island, even just leaving in the morning and coming back at night.  Tinos is good if you want a taste of traditional Greece.  The town is very small though.  Syros has some BEAUTIFUL sandy beaches and buses to take you to them.  I didn’t go to Santorini but I hear it is incredibly beautiful.

Thank you so much for all of your advice and i will definitely try to cut out some places or maybe extend the days longer [image]http://www.eurotrip.com/forum/micons/m16.gif[/image]
 
Is there any way to book some of the flights ahead of time or just wing it when we get there?

 
Sure, you can book ahead of time, check out www.whichbudget.com , www.europebyair.com or www.easyjet.com  for some commong budget carriers
 
 

I would definitely change things around if you want to spend more time on the islands. It is not that difficult to get around in high season, but you can’t necessarily go to the exact island you want, whenever you want, and even during high season, you might have a problem on Sundays. Obviously, if you have more time, you have less constraints. I agree about getting your ticket out as soon as possible.
I would not spend less than a day in Athens, but that’s just me. I wish we had been there long enough to go to Delphi.
We did not book our flight from Corfu to Crete until we were in Venice.
It worked out fine.
We used Europebyair for our ’06 trip, and that worked out fine too—that was ahead of time.

My two cents

You need to change the Greece portion of your trip.

1. 3 days is too much time for Athens.  I still highly recommend you visit the city, but you can see everything the historic city center has to offer (Acropolis, Agora, Roman Forum/Agora, Temple Olympian Zeus and Hadrian’s Arch, Hadrian’s Library and Tower of the Winds, renovated Plaka/Thesseio disitricts, Monastiraki, National and Zappeion Gardens, etc) all in one day.  I recommend 2 days for logistical reasons.  No reason for 3rd day.

2. If you plan to arrive in Greece by ferry from Italy, keep in mind that the commute from Venice to Athens is LONG.  Since almost all Italy-Greece ferries make a stop in Corfu (northwest Greece), and since Corfu is fabulous (and has amazing beaches), I highly recommend breaking your commute there.  (Otherwise, you can fly direct Venice-Athens).  Just because Santorini, Mykonos, and Athens are the only places in Greece known outside of Europe, doesn’t mean that they are the only 3 places in Greece.  As Cil says, Mykonos and Santorini belonging to the same island chain are similar architecturally, being in the same island chain.  The difference between them is that Santoríni has the spectacular volcanic/cliff setting, and Mykonos is better known for nighlife (although Santoríni definitely has young nightlife too).  Syros is excellent place often overlooked.  Also located in the Cyclades island chain, it’s a little different because it was a wealthy island in the 19th century, hence a rather large neoclassical city that was built on the island. 

My advice for the Greece portion of your trip is:

1. Arrive at Corfu from Italy.  Stay in Corfu 3 days (and if you stay at Pink Palace hostel, please make it an effort to leave the hostel and see the island’s beautiful countryside and main town.  There are daily buses to the main town.  You can catch a bus back, or take a taxi cab if it’s after bus hours)
2. fly or overnight bus to Athens (there will be one ferry crossing: Corfu/Kérkyra-Igoumenítsa, included in price of bus ticket.  Pink Palace operates its own buses to/from Athens if you stay with them.) Stay in Athens 2 days, or 2 days one night.
3. fly or ferry to Santoríni OR Mykonos OR Syros OR Rhodes OR Crete (the city of Chania is wonderful).   
4. fly or ferry back to Athens to fly home

Italy/France:

I recommend one of two options:

Adding an extra day to Italy, taking a day off of each Venice and Rome, and allocatng those 3 days to somewhere on the coasts of Liguria (Cinque Terre a good option) or anywhere in Toscana region, maybe basing yoursself in Florence, and exploring the rest of the region.  OR, spending those 3 days further south in Italy, maybe Amalfi/Positano/Praiano, then ferry to Greece from Bari or Brindisi

OR

Taking a day off of each Venice and Rome, and adding it to France’s Provence-Alpes-Côte d’Azur or region (visit Menton, Grasse, Arles…) or add 2 days to Cannes, or allocate one adidtional day to Cannes and the other day to Paris (and use that day for a day-trip from Paris), or make a stop at Dijon (Bourgogne region) on your way to Cannes.