Lavender is a very calming and soothing herb. It's great for sleep troubles- my mother used to have a lavender scented pillow. Too much could be overpowering, though. Also, English lavender is a lot stronger aromatically than French lavender, which is much more mild.
Dandelions are a good diuretic (urine inducer)- in some countries, it is sold medically for this purpose. As Brysing said, they are good for the liver and the leaves in salads. In addition, the leaves have many vitamins: Vitamin A, C, Potassium, Calcium, and Iron. The white 'milk' can also treat warts. Metaphysically, dandelions represent clarity and illumination.
As always, be cautious with any herbs you use. If you have sensitive skin or allergies you should check if using these herbs would be appropriate.
For tea and coffee, it would really depend on the type of tea. But coffee is known for being a stimulant. It can become addictive. My mother always said it helped with nightmares, but perhaps that is just an old wives' tale! Apparently you can treat cellulite with it, but apart from that I don't know much else.