I used to be a LA chowhound but relocated to Boston a few years ago.
Italian - For quintessential Italian in Boston, I would go to Daily Catch (North End...don't go to the others) or Giacomo's (go to the South End location where you can make reservations unless you want to wait in line for 2.5 hours in the North End...food quality is the same).
Lobster Roll - Hot one at Neptune's ($25). For a cheap one, James Hook ($12). i'd suggest going for lunch. Neptune's doesn't take reservations so the wait times can easily exceed 3 hours for dinner. Alive and Kicking Lobsters in Cambridge has a lobster sandwich.
General seafood - Neptune's for their raw bar. B&G has good seafood but I think they're over-rated and over-priced.
Clam Chowder - It's the only thing Legal's does right.
Breakfast - Stephanie's on Newbury for nice atmosphere and proximity to the Commons. For tasty and large breakfasts, consider Ball Square Cafe in Somerville or Center Street Cafe in JP. Also, Mike and Patty's.
Pizza - Fiorella's in Newton has great wood oven pizza. I've heard that Oggi in Harvard Square has good pizza but I've never been there.
Steakhouse - I'm very indifferent to steakhouses. I thought that BOA in LA was a decent steakhouse and I can't think of anything in Boston that has amazing, to-die-for steak. I mean it's all the same beef shipped in from the midwest, right? If you have a car, the Hilltop Steakhouse is always on every Food Network list for the virtual size of the establishment. Never been there myself.
French - I disagree with everyone's review of Hamersley's. They suffer from a lack of consistency in both food and service. For French, I'd head to Craigie on Main (more refined) or Saltz (more wholesome). I recently had the roast duck for 2 at Saltz and it was delicious.
Italian food here far exceeds what you can get in LA so I'd spend my calories consuming that. Valentino's in LA was quite good for fancy fare. There was also a place in Thousand Oaks somewhere I loved.
I moved from the LA area 2 years ago. What happened to Palais des Thes on Canon Drive? When you look them up, it now sends you to Le Palais Gourmet. I'm assuming it's another brand of tea? If so, are they as tasty?
What is a reliable restaurant that you go to because you always know you'll have a good, solid meal? Your default restaurant.