Just The Tip (The tooltip that is)

style.css

.TooltipContainer { position: absolute; z-index: 100; font-size: 10px; display: none; background: #333; color: #fff; -moz-border-radius: 3px; -webkit-border-radius: 3px; -o-border-radius: 3px; -ms-border-radius: 3px; border-radius: 3px; box-shadow: 0 2px 5px 0 rgba(0,0,0, .4); }
	.TooltipContainer .arrow { position: absolute; bottom: -4px; left: 15px; z-index: 1950; background: #333; height: 10px; width: 10px; -webkit-transform: rotate(45deg); -moz-transform: rotate(45deg); }
	.TooltipContainer .content { padding: 5px; position: relative; z-index: 2000; }

tooltip.js

/**
 * tooltip.class.js
 * Requires: jQuery, class.js
 * 
 * Just the tip.
 *
 * Usage:
 * 		var tooltip = new TooltipClass( [options] );
 * 
 * Options:
 *		selector (string): Overrides default tooltip selector
 *
 * Data Values:
 * 		data-tooltip: Content to be displayed in tooltip
 */

dmjs.TooltipClass = Class.extend({
	defaults: {
		selector: 'a[data-tooltip]'
	},
	init: function(options) {
		var self = this;
		this.options = $.extend({}, this.defaults, options);

		this.windowWidth = $("html").width(), 
		this.bodyWidth = $("body").width(),
		
		$(this.options.selector).live('mouseenter.tooltip', function(e) {
			var element = $(this);
			self.show(e, element);
		});
		
		$(this.options.selector).live('mouseleave.tooltip', function(e) {
			var element = $(this);
			self.hide(element);
		});
	},
	show: function(e, element) {
		var self = this;
		this.tooltipElement = $('<div><div class="arrow"></div></div>')
			.addClass('TooltipContainer')
			.appendTo('body')
			.show();
		this.tooltipElement = $('.TooltipContainer');
		this.tooltipContent = $('<div/>')
			.addClass('content')
			.html(element.data('tooltip'))
			.appendTo(this.tooltipElement);

		$('body').bind('mousemove.tooltip', function(e) {
			self.updatePosition(e);
		});
	},
	hide: function(element) {
		$('body').unbind('mousemove.tooltip');
		$('.TooltipContainer').remove();
	},
	updatePosition: function(e) {
		this.tooltipElement.css({
			left: e.pageX-(this.windowWidth-this.bodyWidth)/2-18,
			top: e.pageY-45
		})
	}
});