Ajax!!
A lot of talking about AJAX is taking place here and there; AJAX is the acronym of "Asynchronous JavaScript and XML", a technology based on XMLHttpRequest, which is now supported by all main browsers. The basic idea is quite simple - and not actually a breakthrough - but it allows updating a page following a server request, without reloading the entire set of data. Some examples can be found on GMail or Google Suggest. For additional information about AJAX, you can see Wikipedia.