Is there an optimal font size / line height ratio?

When styling text on web pages, both font size and line height can be set. For example, the text of this post will be displayed using a font-size of 14px and a line-height of (about) 18px, set using the value 1.3em.

Looking at other websites, it seems that a ratio around 1.2 is a common practice.

What is the best practice regarding this? What are some good resources from which I can learn more on the subject?