Scripturizer plugin by xaglen, laurenceo and chipbennett 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 John 3:16
Online Bibles currently supported are:
The NET Bible
The English Standard Version
Oremus Bible Browser
Septuagint Greek OT / Nestle-Aland 26th ed. Greek NT
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.
Download and Info: http://wordpress.org/extend/plugins/scripturizer/