Use the rel="tag" attribute.
- <a href="http://technorati.com/tag/[tagname]" rel="tag">[tagname]</a>
- <a href="http://apple.com/ipod" rel="tag">iPod</a>
- <a href="http://en.wikipedia.org/wiki/Gravity" rel="tag">Gravity</a>
- <a href="http://flickr.com/photos/tags/chihuahua" rel="tag">Chihuahua</a>