I've just discovered a much needed plugin for WordPress: The scripturizer.php.
Straight from the readme:

Scripturizer will convert Bible references in your posts and comments into hyperlinks to online Bibles.

For example, it will change John 3:16 into something like
<a href=";">John 3:16</a>

Online Bibles currently supported are
* Bible Gateway
* (the NET Bible)
* The English Standard Version
* Oremus Bible Browser (the New Revised Standard Version)
* Nestle-Aland 26th edition Greek New Testament
* The Septuagint Greek Old Testament

You can customize the plugin to use your favorite Bible translation or to include links useful for users
of Logos Bible Software by editing scripturizer.php and adjusting the configuration parameters near the
top of the file.