In my city (Lowell, MA) there's everything.
Pizza: Conrad's. Literally 2 blocks away from my house and they will make you anything, even if it's not specifically on the menu.
Asian: Southeast Asian Restaurant (that's the actual name). They have everything from Cambodian to Vietnamese.
Greek: Olympia. Location is a bit iffy, but the food is well worth it.
Italian: Caffe il Cipresso. Technically this is in Tyngsboro, but by far the best. Everything is made when ordered and is all made in-house. I love the Ravioli al'aranccio.
Spanish: Cafe Madrid. Everything there is incredible. I love their seafood paella, so colorful and tasty. The chef hails from Barcelona (I was a little disappointed that his name is not Manuel).
American: Garrison's. This is actually in Billerica, but this is my go-to place for comfort food.
Breakfast: Vic's Waffle. Breakfast all-day, and their specials are terrific. They do have lunch menu, but I've never tried it.
Subs: Captain Jason's. This is just down the street from my house, and they load the hell out of their subs. If you want a meal to feed a couple people, get the fish and chips or haddock dinner. I swear they managed to cram an entire haddock into that carry-out box last time.
Mexican: La Carreta. OK, this is in Nashua, NH; but, it is well worth the trip. Great drinks, food, staff, ambience, etc.