What isn't it good for? Aromatherapy can be used as a mood-enhancer (think of all the creams scented with lavender that are meant to relax you, and the "energizing" face washes scented with citrus), as a healing agent (my mother uses lavender to heal any burns, and it works wonders—just make sure you get Lavandula angustifolia, and not Lavandula vera, which is better for balancing female hormones), as a cleanser (tea tree oil is one of the best antiseptics around) and even as a pain reliever (peppermint) and anti-depressant (geranium).
Whether you're looking for clarification (eucalyptus oil), awakening (try orange or grapefruit oil in a little dish in your shower or over a flame in your bathroom), calming (lavender and vanilla are soothing) or sexyfying (yes, I made that word up, but try ylang-ylang or jasmine in massage or a bedside diffuser and see what I'm talking about), aromatherapy can help.
Here's a quick list of some more popular scents and their uses:
Uplifting and relaxing, it can be used as a purification agent in skin cleansing, taken internally to soothe indigestion or as a home deodorizer.
For pain and insomnia relief, and it can be helpful for balancing hormones. Should be used topically on the skin.
Relaxing, soothing to muscle aches. People often drink chamomile tea for the same reason, but you can drop this essential oil in a cup of hot water or apply it topically to your skin.
Stimulating and uplifting. Taken internally, it helps to promote good digestion and immune health.
Used as an antiseptic, this is my family's secret weapon against canker sores. Simply swill a mouthful of water plus a drop or two of myrrh in your mouth for 30 seconds twice daily and watch them disappear!