Ivtv devices (cx23415, cx23416)
The ivtv devices have built-in hardware compression. They include the Hauppage PVR-150, 250, 350, and 500 cards; for a full list, see supported hardware.
Since the ivtv devices have their own wiki, there is no need to duplicate the effort here.
However, note that the ivtv code has now been merged into the v4l tree. It was submitted for inclusion in the 2.6.21 kernel on 1 March 2007, but appears not to have been accepted yet (as of mid-April 2007), which likely means it won't be included until 2.6.22. It is in Andrew Morton's mm experimental kernel.