Chamomile is wonderful. It's easy to grow and fresh chamomile is so much better than the dried stuff. You pick the flowers- I like putting them in an individual french press type cup. The flowers are pretty.
Since dried flowers aren't nearly as nice, this year I'm going to pick the flowers, wash them, and freeze them in ice cubes. When I want fresh chamomile tea in the winter I'll just put on of the cubes in a cup and add hot water.
My other favorites are lemon grass, basil, lemon balm, lavender and anise seed.
My all time favorite, though, is one I can't have anymore due to an allergy. Fennel tea. You put a teaspoon of seeds in a cup, add hot water and let steep. When you get a seed in your mouth, eat it. You should actually eat all the seeds. It calms the stomach, and if you have a cup of tea a day, you'll get the fiber you need to keep things moving smoothly.
It's amazing the things you can grow in your garden that make great teas. It is best though to check each one online in case there are any side effects to having too much. Many herbal teas are medicinal.