.attr({checked: e.target.checked ? "checked" : ""});

to

.attr({checked: e.target.checked });

You don't need the "checked" or "", simply true or false with attributed checked is good. People also need to understand that the first "checked" is a string not a variable (for those who didn`t know). Using "checked" and "" instead of true or false, was making my code bug thus i couldn't uncheck my boxes.

(function ($) {
    $.fn.enableCheckboxRangeSelection_custom = function () {
        var lastCheckbox = null;
        var $spec = this;
        $spec.unbind("click.checkboxrange");
        $spec.bind("click.checkboxrange", function (e) {
            var alreadyChecked = true;
            var currentTarget = e.target;
            if (typeof currentTarget.htmlFor !== 'undefined')
            {
                currentTarget = document.getElementById(currentTarget.htmlFor);
                alreadyChecked = false;
            }
            if (lastCheckbox != null && (e.shiftKey || e.metaKey)) {
                var elements = $spec.slice(
                Math.min($spec.index(lastCheckbox), $spec.index(currentTarget)),
                Math.max($spec.index(lastCheckbox), $spec.index(currentTarget)) + 1
                );

                //begin added by Laszlo
                elements.each(function(index, elem){
                      var _name = $(elem).attr("name");
                      //you can do anithing with jQuery here, call other functions, etc...
                  }
                //end added by Laszlo

                });
                if (currentTarget.checked == alreadyChecked){
                    elements.attr({ checked:"checked"});
                }
                else{
                    elements.removeAttr("checked");
                }

            }
            lastCheckbox = currentTarget;

            //Hack: Reset the value of the input when a label is clicked and then trigger the click of the input self. Now this solution is compatible with events on that input (like a custom change event)

            if (!alreadyChecked && (e.shiftKey || e.metaKey)){
                e.preventDefault();
                if (currentTarget.checked == true){
                    $(currentTarget).removeAttr("checked");
                }
                else{
                    $(currentTarget).attr({ checked:"checked"});
                }
                currentTarget.click();
            }

            return true;
        });
    };
})(jQuery);

don't forget to init the function when document.ready:

$("input:checkbox").enableCheckboxRangeSelection_custom();

I experimented a lot these 2 days to get the same behavior gamail uses and figured out how to get a correct implementation. Be aware: The code is much longer :(

Solution is cross browser compatible

(function ($) {
    $.fn.enableCheckboxRangeSelection = function () {
        var lastCheckbox = null;
        var $spec = this;
        $spec.unbind("click.checkboxrange");
        $spec.bind("click.checkboxrange", function (e) {
            var alreadyChecked = true;
            var currentTarget = e.target;
            if (typeof currentTarget.htmlFor !== 'undefined')
            {
                currentTarget = document.getElementById(currentTarget.htmlFor);
                alreadyChecked = false;
            }
            if (lastCheckbox != null && (e.shiftKey || e.metaKey)) {
                var elements = $spec.slice(
                Math.min($spec.index(lastCheckbox), $spec.index(currentTarget)),
                Math.max($spec.index(lastCheckbox), $spec.index(currentTarget)) + 1
                );
                if (currentTarget.checked == alreadyChecked){
                    elements.attr({ checked:"checked"});
                }
                else{
                    elements.removeAttr("checked");
                }
            }
            lastCheckbox = currentTarget;

            //Hack: Reset the value of the input when a label is clicked and then trigger the click of the input self. Now this solution is compatible with events on that input (like a custom change event)

            if (!alreadyChecked && (e.shiftKey || e.metaKey)){
                e.preventDefault();
                if (currentTarget.checked == true){
                    $(currentTarget).removeAttr("checked");
                }
                else{
                    $(currentTarget).attr({ checked:"checked"});
                }
                currentTarget.click();
            }

            return true;
        });
    };
})(jQuery);

if (lastCheckbox != null && (e.shiftKey || e.metaKey)) {
  ......
} else {
  lastCheckbox = e.target;   <-----
}

Cool. Attribution is perfectly fine as-is. I'm not a licensing nazi, even though I probably should be.

I made a slight modification, namespacing the click event (so it can be unbound unambiguously) and unbinding it before reapplying.

http://pastie.textmate.org/316003

I have checkboxes in drag-and-drop sortables. This way, I can re-apply enableCheckboxRangeSelection after sorting to get the order right.