San Antonio's resident certified permaculturist Doddi Evans has been talking about herb spirals recently. He's planning to have a workshop to build one soon. Until you make that event here are two youtube videos on two different herb spirals.
This video is by certified permaculturist Scott A. Meister of Japan's Potato House Permaculture Pension.
This video shows a different design by Dick Pierce which uses lots of straw as a growing medium , Dick is an Austin permaculture design consultant.
Finally, here is a video tour of a mature spiral by solealunaduir. It will give you an idea of how lush an herb spiral can become.