You can get all the timetables for Italian trains at Trenitalia official site here.
The website is both in Italian and English. To see the price of the ticket click on the "buy" icon. I suggest not to buy via internet, since the service is quite crappy, as usual with Italian trains! ;-)
For information in German you can also use DB site here.
Remember to validate the tickets before gettin on an Italian train. There are usually yellow validating machines at any track inside the station, use them!
InterCity and Eurostar trains have a "supplement" tariff, you have to tell the ticket office man/woman that you are going to take an IC or ES. On ES the reservation of the seat is mandatory, while on IC you can reserve or not. If you do it costs you 3 euros more.
Italian trains are often late, so prepare to have a lot of patience! ;-)
You can check routes and timetables of Eurolines buses in Italy here. The site is in Italian and English.
For buses to/from airports check on the airports' homepages.
For urban buses check on the towns' internet sites.
Airports are usually connected to the main towns by bus. The only Trenitalia connection is available in Pisa and Roma Fiumicino.
Stay away from Alitalia if you are a low-budget traveller! Domestic flights are served also by AirOne (Lufthansa group), Meridiana (which claims to be low-cost, but it isn't) and recently also RyanAir.
Many low-cost airlines land in Italy, the most famous are RyanAir, Easyjet, Air Berlin, Hapag Lloyd Express, Germanwings, Wizz Air, SkyEurope, MyAir (former Volare)...
Low-budget "hubs" are Milan "Orio al Serio" (which is actually in Bergamo) and Rome "Ciampino".
High-budget "hubs" are Milan "Malpensa" (which is actually close to Varese) and Rome "Fiumicino".
The most important ports for ferries to Sardinia and Corse are: Genova, Livorno and Civitavecchia.
You can check timetables and prices at Tirrenia, Moby and Corsica Ferries sites.
For the Isola d'Elba you take the ferry in Piombino (Livorno).
In Italy you have to pay to drive on motorways (Autostrade). Maximum speed limit for cars is 130Km/h. Fastened seat belts are compulsory in all the roads.
Hitch hiking is not allowed on motorways, so be careful if you travel this way, the Police could not like it!
Roads in Italy are usually in decent conditions; snow tyres or wheel "chains" are mandatory in Winter in many regions.
There is no leaded fuel anymore, only unleaded (95 and 98 octane) or diesel are available. Self-service is usually cheaper at gas-stations.
Motorbikes have to turn lights on at any time of the day. Helmet is compulsory.