Gina,
I'm yet to have been to Venice and it's been a long time since I was in Milan. I'm not a big fan of Florence, though it is of course spectacular, and much prefer Siena. But I should mention that La Garga, mentioned in the previous post by Dom, I visited quite some time back and it was excellent (I wrote something about it in the thread on Rome and Florence linked to above).
For some additional specific restaurant suggestions, I suspect Choey might have some excellent ones to add to the impressive list from Dom; hopefully he'll see the thread and chime in. For my part, I've had over the course of many visits, both short and fairly extended, only one genuinely bad meal in Italy and only a handfull of mediocre meals where I left wishing I hadn't wasted the calories. One thing I do is the obvious, though not always convenient -- namely avoid dining in obvious tourist joints and more generally avoid dining in tourist areas. Obviously, in parts of Rome and much of the core of Florence that's hard, but in Rome I've had few problems finding places that are frequented heavily by locals.
If all this is completely obvious, please forgive me. The same goes for the following...
***
Now, if I were about to embark on a trip to Milan, Venice, Florence and Rome, what would I want to eat? Well, of course, I'd always be keeping an eye out for the new or the unusual, but there are some regional specialities that I either really like and always have when I go to the region in question or haven't gotten around to trying yet in the area whence they come. Now, sitting back at my desk, contemplating the trip, this is what comes to mind as things I'd like to eat...
Milan
• risotto alla Milanese
• osso buco
• goose
• büsêca (Milanese style tripe)
• pizzoccheri (buckwheat noodles, specialty of the Valtellina, north of Milan)
• polenta with luganega (fresh local sausages)
• tortelli di zucca (pumpkin-filled pasta)
• local cheeses (Gorgonzola, Taleggio, casera, bitto, Stracchino)
• local cured meats (bresaola, salame di Milano, cacciatorino)
Venice
• risotto nero (black risotto)
• risi i bisi (rice with peas)
• risotto cogli asparagi
• insalata di mare (salad of baby octopus, squid, mussels, etc.)
• bigoli in salsa (local style of fresh string-like pasta with anchovy sauce)
• baccalà alla vicentina (salt cod with milk, garlic, parmesan, nutmeg, usu. with polenta)
• seppie alla veneziana (cuttle fish cooked in lemon and wine, served usu. with polenta)
• fegato di vitello alla veneziana (traditional, simple liver dish)
• duck (bigoli co l’Anara!)
Florence
• schiacciata coi siccioli (flat bread with pork cracklings)
• bistecca alla fiorentina (grilled steak)
• arista alla fiorentina (pork roast)
• lattonzolo (suckling pig, traditionally slaughtered in early summer, I believe)
• cinghiale alla cacciatore (boar, hunter style)
• local cured meats (finocchiona – fennel salame, buristo – blood sausage, capocchia)
• local pecorino for the cheese course!
• rabbit
Rome
• carciofi alla romana
• carciofi alla giudia
• puntarelle con le alici
• pizza bianca
• gnocchi di semola alla romana
• fettuccine alla romana
• rigatoni con asparagi e ricotta
• rigatoni con la pajata (intestines)
• coda alla vaccinara (oxtail stew)
• trippa alla romana
• lamb
Make one meal in each place a selection of local cheeses and cured meats and bread and cheap wine bought in little shops and consumed outside and you will be happy. A good Swiss knife is useful (pack it in your checked luggage

).
Again, insofar as the above is obvious, I apologise; otherwise, if you have any questions about the above items, feel free to ask.
I hope you have a great trip... (I'd bring some loose fitting clothes ...

)...
Antonius
Alle Nerven exzitiert von dem gewürzten Wein -- Anwandlung von Todesahndungen -- Doppeltgänger --
- aus dem Tagebuch E.T.A. Hoffmanns, 6. Januar 1804.
________
Na sir is na seachain an cath.