Top of the list is bread, no question. Nothing else comes close.
I am going to amend my response, if I may, to include toast.
Very underrated scent.
mmm
Onions frying in fat.
Curry of any sort. (I was making Japanese curry a couple weeks ago and my five-year-old walks in and says “what are you cooking? that smells so good!” This is my daughter who currently has a diet consisting of like six things, which seem to rotate out every few months. As I wasn’t making that for the kids, I used the medium-hot cubes – which are not super spicy, but they have a little kick. She tried some and loved it! So I stocked up on some mild Vermont Curry cubes, as Japanese curry is one of my favorite low-stress weekday dishes to make, and very homey to boot.)
Bacon. I don’t eat a lot of it – less than monthly – but its smell will always draw both my daughters to the kitchen like puppies begging for food.
Bread, of course.
My wife, meanwhile, just doesn’t like the smell of anything cooking wafting into the rest of the house, so I generally have to keep the kitchen door closed when I cook. For me, that’s the smell of home, and my memories of many people are tied to the smells of their homes and the foods they cook.
Ooh, so many good choices. I can’t pick one.
I have to say, yesterday, every time I entered the part of the house that smelled of cooking, I thought “wow, that smell of roast turkey is good”. I don’t even like turkey all that much, but it smelled wonderful.
Toast is a good choice. So is frying onions. And baking cookies. And roast chicken or duck, if they aren’t overpowering. Mmmm. I guess I’m a sucker for malliard reactions.
Chocolate chip or peanut butter cookies. Cinnamon rolls. My 12 cheese lasagna.
Not around our house. We are pretty lazy cooks. Pretty often, if one or the other or us is just a mite peckish, we’ll have a couple of pieces of toast w/ butter. Ivariably causes the other to have a couple as well.
Yeasty bread smell
Chocolate, chocolate and chocolate in that order.
Apple pie. Since I don’t bake, I make do with apple pie scented candles. In the winter, I burn them every day.
Bread. My potluck contribution at work was fresh baked bread. I’d bring in the breadmaker loaded ingredients and start the show under my desk. Garlic parmesan bread. The office would be going wild after a couple of hours.
And french fries. I can smell a fast food place seemingly miles away from this scent.
Good one!
Saffron. I like to chuck it into a pot of lentils a few times a year. Makes the apartment smell like home.
Vanilla is another that smells great. It brings together the flavors in a dessert I used to make with peaches, cherries, cinammon, honey and other good things.
And sesame oil. The aroma doesn’t last long, though, because I add it just before eating.
This is all kinds of awesome.
mmm
Most of the above, but I didn’t see sautéed onions and bell peppers mentioned! That is the most common smell in my kitchen, and foreshadows so many good things to eat.
I don’t know much about preparing fried chicken, but I think she would remove the skin, dip it in something (IDK) and then roll it in cracker meal. Then pan fried in about a half-inch of oil, so I guess I need to amend my entry to read, My Mom’s pan-fried chicken.
Mom also used to make Butter-Nut Pound Cake and the B-N flavoring was 10 times better smelling than vanilla – not that there’s anything wrong with vanilla aroma. Just don’t taste test either.
Bacon
A turkey as it approaches the midway point toward doneness
Oven-baked pie
Boiling oil at Xmas-time
It has a unique aroma. My mom wasn’t a great cook and I’ve never really missed her cooking, but I had a very strong reaction to the smell of frying chicken the first time I made it myself. After a few minutes, the kitchen was filled with an aroma that stunned me for an instant until I made the connection. I think it’s because of the bones and whatnot and the shortening. Most recipes call for big pieces with skin and up to 20 minutes of deep frying. I prefer smaller pieces without bones or skin and pan frying in olive oil. Easier, less mess and probably healthier, but it doesn’t have that unique aroma.
Freshly baked bread is number 1 on the list. Or anything that is bready and yeasty.
Anything being baked with cinnamon and/or ginger.
Lasagna, garlic cheese bread, pizza
Coffee - although I don’t drink it
HATE, HATE, HATE the smell of frying onions and green pepper. Bacon too. Lingers way too long.
Hate hate hate the smell of cooked (or cooking) bell peppers, but I like the smell of cooking onions.
I prefer not to sit next to someone eating a stuffed pepper, for instance. It will ruin my meal.
Oy, I should have such problems! 
Garlic sauteeing in EVOO was the first thing that came to my mind, but I agree with all of the above.
Has homemade pizza fresh out of the oven been mentioned? Or onions and garlic sauteeing in lard with paprika?
How about thick-cut French fries and onion rings deep-fried in lard?