WDTV Live really impressed me a couple years ago first time I saw it. If you want something that works as well as WDTV but also want library scraping, XBMC on any new tiny-formfactor atom/ion computer should do it for about 30w. A heck of a lot less than xbox/ps3 + transcoding computer.
I use XBMC daily, though I have a NAS that holds the media, which consumes another 24w or so. *Still* less than my xbox at idle.