The Archos 5 is Android-based and connects to a TV via HDMI. All the usual Android apps are available on the screen, you can watch (and download) video, and you can connect a Bluetooth keyboard and mouse. So I think we are there, actually.
(The device then detaches from the TV dock and is a portable media player / Internet tablet. It was buggy at first, but I am liking it a lot now.)
When I saw the Litl (before Chrome OS was revealed) I thought that it would make a pretty good AppleTV competitor, with the added benefit that when not in use in that way it would act as a portable web access device.
(Though as far as I can tell, neither Litl, nor Google are pushing their devices in this way. Though it wouldn't be too hard to stream your audio and H.264 video via the web onto ChromeOS)
