Sticks an element to the top of the window after scrolling past it.

jquery-stickybox.js

/**
 * Copyright (c) 2011 Tristan Waddington <tristan.waddington@gmail.com>
 *
 * Permission to use, copy, modify, and distribute this software for any
 * purpose with or without fee is hereby granted, provided that the above
 * copyright notice and this permission notice appear in all copies.
 *
 * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
 * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
 * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
 * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
 * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
 * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
 **/
(function($) {
    var settings, elem, offset;

    $.fn.stickybox = function(options) {
        if ($(this).length > 0) {
            elem = $(this);
            offset = elem.offset();

            // Override defaults
            settings = $.extend(default_settings, options);

            // Update initial position in case the page loaded below the offset
            update_position();

            // Register scroll handler 
            $(document).scroll(function() {
                update_position();
            });
        }

        return $(this);
    };

    update_position = function() {
        if ($(document).scrollTop() >= offset.top) {
            elem.addClass(settings.stuck_class).css({
                'display': 'block',
                'position': 'fixed',
                'width': '100%',
                'top': 0,
                'left': 0,
            });
        }
        else {
            elem.removeClass(settings.stuck_class).css({
                'position': 'relative'
            });
        }
    }

    var settings;
    var default_settings = {
        'stuck_class': 'stickybox-stuck'
    };
})(jQuery);