Tea tree and peppermint are my all time favorites. Here's what I use peppermint for (off hand!):
When someone has a bruise, (like my two year falling and getting a knot on his head) I put a drop right on the spot. Relieves pain and reduces swelling ... QUICKLY!
When someone has a tummy ache, I put a couple drops in a glass of water and have them drink it. (aids with digestion)
When air freshener is needed, I keep a water bottle with a few drops of oil in it ~ Refreshing!
When we need to use the vaporizer, I add a few drops ~ helps with congestion.
For as quickly as I go through it, I know there are more uses I can't think of! It smells delightful and works wonders!