The allium family
A real head of garlic, before cleaning it up for storage
I guess you could also include chives, but we talk about that in the herbs section.
The one thing we don't grow are onions themselves! We haven't considered them to be worth using some of our limited garden space since home-grown onions aren't that different from purchased onions, which we can get at the regional market.
In Summer 2013 we planted a walking onion, sometimes called Egyptian onion. We put it in among the blueberry plants. Note the top bulbules that are resting on the ground above the main bulb. They set down roots evidently and become new plants.