Perennial herbs are herbs that continues to grow year after year. Choose a hardy plant and make sure you check your growing zone to see if your herbs will last through the winter in your area.
Here's some popular perennials to grow:
Mint
Sage
Echinacea
Thyme
Lavender
Chives
Rosemary
Oregano
Detailed list of Perennials:
http://www.gardensablaze.com/Perennials/PerennialHerbs.htm
