Excellent domain search tool, ajaxified, and supports multiple (even configurable) extensions, probably not 100% reliable though if it relies on whois.
Mibbit is an ajax client for IM networks (IRC and Yahoo). You can log on via the site. They pass on your IP to avoid spam / abuse / etc.
Kayak allows you to search multiple flight / holiday web sites and filter the results using some very cool ajax.
Online AJAX Solitaire through your browser, no plugins required!