Apple's Knowledge Navigator
In 1987, Apple produced a futuristic concept video (Google Video link) showing their vision of the future of computing in the year 2010. The video featured a laptop-ish computer which embodied several major advancements, chief among them a natural-language spoken interface -- not just voice-controlled, this interface was conversational.
Aside from the (still sci-fi) verbal interface, many of the other innovations have come to pass, at least in some form: wireless networking, effective internet searching, internet-based videoconferencing, lightweight large-screen portable computers, and touch screen interfaces are all commonplace today, two decades after the video was produced.
Further reading: Wikipedia page on the Knowledge Navigator (mentions a second K.N. video that I couldn't find online); high resolution QuickTime versions of the Knowledge Navigator video; Future Shock, another Apple concept video from 1988; Alan Kay's Dynabook (an early laptop concept).