The Sticky Scroll Sidebar plugin is designed to allow an element to stick to the top of the screen as page scrolls down, but without moving outside of the parent container.

sticky-scroll-sidebar-within-content.js

/**
 *  Plugin for sticky scroll sidebar within content.
 */

// Utility : Object.create dosen't work all browsers.
if ( typeof Object.create !== 'function' ) {
  Object.create = function( obj ) {
		function F() {};
		F.prototype = obj;
		return new F();
	};
}

(function( $, window, document, undefined ) {

	var StickySidebar = {
            init: function( options, elem ) {
                var self = this;
                self.elem = elem;
                self.$elem = $( elem );
                
                /* Update Options */
                self.options = $.extend( {}, $.fn.rtStickySidebar.options, options );
                
                /* Function */
                self.StickyScroll();
            },
                    
            StickyScroll: function() {
                var self = this;
                var $window = jQuery(window);

                $window.scroll(function () {
                     
                    if ($window.scrollTop() > (self.$elem.parent().offset().top) &&
                        (self.$elem.parent().height() + self.$elem.parent().position().top - self.options.bottomspace) > ($window.scrollTop() + self.$elem.height())) {
                        self.$elem.animate({
                            top: ($window.scrollTop() - self.$elem.parent().offset().top + self.options.topspace) + "px"
                        }, {
                            queue: self.options.queue,
                            easing: self.options.easing,
                            duration: self.options.duration
                        });
                    } else if ($window.scrollTop() < (self.$elem.parent().offset().top)) {
                        self.$elem.animate({
                            top: "0px"
                        }, {
                            queue: self.options.queue,
                            easing: self.options.easing,
                            duration: self.options.duration
                        });
                    }
                });
            }
        };

	$.fn.rtStickySidebar = function( options ) {
		return this.each(function() {
			var stickysidebar = Object.create( StickySidebar );
			stickysidebar.init( options, this );

                        /* Store Data */
                        $.data( this, 'rtStickySidebar', stickysidebar );
		});
	};

	$.fn.rtStickySidebar.options = {
                easing: 'linear',
                duration: 1000,
                queue: false,
                topspace: 10,
                bottomspace: 10
	};

})( jQuery, window, document );