I've made some minor modifications to the Tooltip plugin to have it integrate with jQuery UI. I'm wondering, though, if this has already been done. I couldn't get it to work reliably with the extraClass option (sometimes the styles didn't seem to be applied in IE anyway) so I extended the options with a uiClasses option that by default is set to "ui-widget ui-widget-content ui-corner-all" and set these as the default class when the tool tip is created. This seems to work reliably, but I don't want to reinvent the wheel, especially if there are things that I've missed in my limited testing.
defaults: { delay: 200, fade: false, showURL: true, extraClass: "", new>>> uiClasses: "ui-widget ui-widget-content ui-corner-all", top: 15, left: 15, id: "tooltip" }, function createHelper(settings) { // there can be only one tooltip helper if( helper.parent ) return; // create the helper, h3 for title, div for url helper.parent = $('<div id="' + settings.id new >>> + '" class="' + settings.uiClasses + '"><h3></h3><div class="body"></div><div class="url"></div></div>')