train from amsterdam to paris

I think what you would need would be a 3-country select Pass for Benelux, France and Italy. (Benelux is Belgium, Netherlands and Luxembourg as one country.)
If I were considering this pass though, I would first figure out what the cost would be to purchase the point-to-point tickets which include reservations to compare with the cost of the Pass and the Eurail Pass reservations which are sold separately.

Florence, for most of those ( if not all, not sure about Florence-Venice-Milan) you will have to pay an extra fee plus your pass.
The Eurorail Pass is often not the most economic or easy way to travel nowadays( it used to much better 20 years ago!).. besides the extra fee you must make reservations for some of those trains. I would sit down and work out the prices for point to point tickets,, of course if you have left it quite late then you will not be getting the best deals as the cheapest prices come out far in advance of date of travel, but it still may work out cheaper and easier to buy some point to points and perhaps even a flight . For instance, From Amsterdam to Paris ,, this july, I am paying 35 euros per person( second class which is perfectly nice on a Thalys!) . I did however purchase my ticket on Thalys in mid April for mid July travel. I also purchased tickets on idTGV , from Paris to Nice for 40 euros( first class too, what a deal) .. Cheap. From Nice I would look at Vueling or Easyjet to fly to Italy,, much easier and can be quite cheap, I am using both airlines this summer also,, and got some great deals. Of course you have to travel light for airlines, but frankly you have to for trains too, there are no porters or luggage service in train travel

Thank you Darcy and Pat for your excellent advice. I will check out all the information you provided. We are leaving on Sept. 1 so hopefully that will give me enough time to decide.

None of these segments are best traveled with a pass. Amsterdam-Paris = buy Thalys tickets in advance, from € 35. Reservation alone costs more on a pass than that - and have strict quotas. The sectors within Italy are best traveled without a pass and advance purchase - make sure to check Trenitalia's competitor, Italo!

Adding to Andre's comment, the Thalys train has one of the highest supplemental fee charges in Europe for Eurail pass holders. Depending on the type of pass you have (includes all countries on the train run or it doesn't), the supplemental fee runs from 30Euro to 50Euro. That's steep. Plus, I understand that Thalys limits seats for passholders and can delay you to a later train. The good news here is that you can actually go online right now and buy a non-refundable, non-exchangable ticket for 35Euro for Sept 1. You really don't need a pass for any part of the journey you describe. You're not traveling that much by train. You can get great fares from Paris to Nice on www.tgv-europe.com. Select Great Britain as your ticket collection country. If you select U.S.A. you will be switched to Raileurope which you don't want. Don't worry. You can print your tickets out at home and you won't be going to Great Britain. I see fares as low as 49Euro to Nice if you book now. In Italy, Trenitalia will charge you a 10Euro supplemental fee on top of your pass for the high-speed runs. Florence/Venice and Venice/Milan are most likely high-speed runs. Again, you can get great fares here if you book early on www.trenitalia.com. I see fares as low as 9Euro on some Florence/Venice runs right now on www.trenitalia.com. The tickets are non-refundable and non-exchangable. Your pass will never match this kind of value. Also, should your plans change, a $12 ticket just won't get in the way.