WordPress.org

You can use this plugin to prevent your site from appearing in the server logs of referred pages as a referrer. The operators of the referred pages cannot see where their visitors come from any more.

For example, this plugin will automatically convert all external links to this format http://anonym.to/?http://example.com.

This is an anonymous link to example.com which prevents the original site from appearing as a referrer in the log files of the referred page.

(Based on the WP Blank Referer by blackhatzen)