My general guideline for flavorings is the same as it is for the foods being flavored: variety, variety, variety. I have about 15 or so flavorings lined up on a kitchen shelf, and I try to use a different one everyday (in addition to some that I use everyday). That is a way of making sure I get a wide variety of specialized substances that the flavorings contain -- if they contain any, that is. If nothing else, at least I get a variety of tastes.
Unfortunately, I usually can't eat any flavorings made from seeds (as described here
http://www.aristotleadventure.com/anti-itis/ ), so I try to maximize the list of flavorings I
can use.
I would like to offer my list in hopes someone here could add to it. (I like hunting for new flavorings.) All are in dry form, and most I can buy economically in bulk in the "natural foods" section of the grocery store I go to.
I have shown below which part of the plant they come from, as far as I know. This process of accumulating flavorings has been educational for me.
basil (from leaves),
chives,
cilantro (leaves),
cinnamon (inside of tree bark),
dill weed (leaves),
garlic (minced),
ginger (roots),
marjoram (leaves),
onions (minced),
oregano (leaves),
sage (leaves),
tarragon (leaves),
thyme (leaves),
turmeric (roots).