A template for creating bookmarklets which load jQuery from the Google CDN - see http://chris.improbable.org/2009/apr/3/cleaning-up-the-web-with-jquery-and-a-little-help/

bookmarklet-template.js

/*
 To avoid polluting the global namespace this uses an anonymous
 function which is called with either the URL for an external
 JavaScript file or a function. In either case jQuery will be loaded
 from the Google CDN before your code is executed so it's free to
 depend on jQuery without checking for it and can do things like
 jQuery.getScript() to load other components (e.g. jQuery UI),
 stylesheets, etc.
*/
(function (target, msg) {
    var loader = function() {
        // Avoid executing this function twice:
        if (arguments.callee._executed)  return;
        arguments.callee._executed = true;
        
        if (typeof target === "function") {
            target();
        } else {
            jQuery.getScript(target);
        }
        
        // Now that we're done with the actual work, let's display a 
        // confirmation message so the user knows it's ready:
        var el = document.createElement('div');
        el.style.position='absolute';
        el.style.height='30px';
        el.style.width='200px';
        el.style.margin='0 auto 0 auto';
        el.style.top='0';
        el.style.left='40%';
        el.style.padding='5px 10px 5px 10px';
        el.style.backgroundColor='#f99';
        el.innerHTML=msg;
        document.body.appendChild(el);

        window.setTimeout( function() { jQuery(el).fadeOut('slow', function() { jQuery(this).remove(); } ); }, 2500 );
    };

    if (typeof jQuery !== 'undefined') {
        // Nice - this page already uses jQuery!
        loader(); 
    } else {
        var s = document.createElement('script');
        s.type = "text/javascript";
        s.setAttribute('src', document.location.protocol + '//ajax.googleapis.com/ajax/libs/jquery/1.2.6/jquery.min.js');

        if (s.addEventListener) { // Mozilla / WebKit
            s.addEventListener("load", loader, false);
        } else if ("onreadystatechange" in s) { // IE
            s.onreadystatechange = function () {
                  if (this.readyState == 'complete' || this.readyState == 'loaded') { loader(); }
            };
        } else {
            // Chances are if your browser is this old jQuery won't even work but just in case:
            window.setTimeout(loader(), 2500);
        }

        document.getElementsByTagName('head')[0].appendChild(s);
    }

// Note the use of document.location.protocol to avoid http/https
// mismatches. Obviously this requires a server such as pantheon which
// can handle either protocol:
})(document.location.protocol + '//path.to.example.com/something.js', "Page Enhanced!");

// If you just need a little jQuery, pass a function instead of the URL to a .js file:
//})(function(){ jQuery('body').append('<p>Hello!</p>'); }, "Page vandalized!");