// ==UserScript==
// @name       Always Open External Links In New Tab
// @namespace  http://use.i.E.your.homepage/
// @version    0.1
// @description  enter something useful
// @match      *://*/*
// @copyright  2012+, You
// ==/UserScript==

var nodeList = document.getElementsByTagName("a");
for (var i=0; i<nodeList.length; i++) {
    var link = nodeList[i];
    if (link.href.indexOf(location.hostname) == -1)
        link.target = "_blank";
}