Google Suggest made a nice service (to me) by introducing the concept of Javascript's XmlHttpRequest, but I don't think that Google Suggest is such a great interface. It's responsive and all, but I don't like the way it uses HTML components. I suppose continous filtering of the actual results—which would be cool—would be too heavy for the servers. But anyhow, XmlHttpRequest is a great technique, and if you're making web applications, you'd better learn it.