In reality, there are two kinds of cinnamon, and what you find at the grocery store may not be the ingredient you're after. There's true cinnamon, which comes from Sri Lanka, and cassia, which is also sometimes called Chinese cinnamon. Cassia is actually the more common of the two, so if you're buying your cinnamon in powdered form, you may actually be buying cassia. Not to worry, though -- gourmands tend to find that cassia has a less complex flavor than true cinnamon, but that it also gives off a much stronger aroma, making it great for brightening the house with the smell of your baking.
One of the best things about cinnamon is how well it pairs with heavy and sweet foods. Dense cakes, heavy creams and black coffee all benefit from a dusting of cinnamon. Unlike most spices, which are best bought whole to keep longer and save money, it's not difficult to go through a bottle of powdered cinnamon before it loses its potency. Sticks of pure cinnamon are handy to have around for stirring hot cider and flavoring curries, but they're difficult to grate, so unless you have your own spice grinder, the powdered variety is fine.