Need help planning cities / order & itinerary!

It's not exactly on the way, but I would take the 3 nights to go to Venice! Venice was one of my favorite places to visit (especially if you go out to Murano, Burano and Torcello). At least spend two nights there, and you can take the third and head somewhere else if you'd like. Or spend two nights in Milan since part of your first day will be taken up just arriving there. You could go up to Como which is beautiful and not far! On another note: personally, Siena's not a place I feel the need to stay in for three nights. I'm sure people can give you suggestions on hotels but I was there for a day on the way to Florence from Rome and felt like I did enough. I went to a few of the churches, saw a lot of art and museums (had a fabulous tour guide who is a professor at my uni) and hung around the piazza for a bit. If you are Catholic there will be a bit more for you to appreciate there, but you may want to look into something else on your way to Rome. Hotels in Rome: I haven't actually stayed there, but I've heard Casa de Fiori is somewhat affordable and a good one. The one I did stay in--Hotel Primavera--it was affordable, but not very nice, but it does have a good location right near the Piazza Navona.

Hi Joie; I would suggest you spend some time in Milan - to see the Duomo and the area around it! Milan has an excellent subway system with 4 'coloured' routes, ( each goes a different direction) and is easy to get around the city. I have never stayed there, but I believe I have heard good reports about a Best Western not too far south of the Duomo a few days ago on this site.
Have a great trip!

IMHO Milan is worth 2 nights since you're going to be there anyway. Duomo (go up on the roof), Last Supper, Sforza Castle, Galleria V. Emmanuele.

Hi Joie. If I may, I'll suggest the following: April 1 - arrive Milan, transfer to Venice April 2 - Venice April 3 - Venice April 4 - Venice April 5 - transfer to Florence April 6 - Florence April 7 - Florence April 8 - transfer to Siena April 9 - Siena/hilltowns daytrip April 10 - transfer to Rome April 11 - Rome April 12 - Rome April 13 - Rome
April 14 - depart Now for some rationale. Yes, a long time in Venice but it is immensely more interesting than Milan. (Stay in Milan of the Last Supper is important to you and if you can get tickets, which is unlikely at thsi late date.) You can take a train from Malpensa to Milan Centrale and on to Venice easily. When you arrive in Venice it will be check-in time. You can shower, take a walk, have dinner and get to bed on local time. Check out Rick Steve's suggested Venice itinerary and take time to savor this amazing city. You can daytrip to Verona or Padova too, as well as the outer islands. I agree with another poster that Siena has only so much of interest, but it is a great base for seeing some hilltowns. Take a bus to Volterra for example. I recommend 4 nights in Rome because there is so much to see! Endlessly fascinating and rich with art and history ands culture. Budget lodgings are tough. Try http://www.vrbo.com for studio apartments, check Rick Steves' guides, compare them on Trip Advisor. We had a great B&B in Venice, http://www.aitagliapietra.com that runs 60 to 95 euros depending on season. In Rome, a lot of people recommend the Beehive http://www.the-beehive.com/ but I have not personally used them. Looks like some excellent options there and well-recommended.

I think Laurel's suggestion is great. For Venice: DEFINITELY go to Murano, Burano and Torcello, the outer islands. Murano has beautiful glass, Burano has lace and bright beautiful houses (http://www.flickr.com/photos/drc09/5386931002/), and while Torcello is small and doesn't have much to do on the island, to me it was worth a visit because it has some great walking and exploring. You can buy a 12 hour (or less) and spend an afternoon visiting the outer islands. Other possible day trips from Siena are Arezzo, Cortona, Montepulciano. Castiglione del Lago if you want to see a beautiful lake area.