I heard a really cool cover to Portishead's "Wandering Star" the other day on KSJS, and today it occurred to me to try to track it down.
Kid Beyond does a pretty cool a cappella version.
I also liked Level's version.
Then I ran across this pretty amazing song after the manner of Portishead, with a pretty cool video to go with it: Nature Boy, by Peach Stealing Monkeys. They have some other cool songs too.
I never did find the cover I was looking for, but the Peach Stealing Monkeys stuff more than made up for it.
Update: Peach Stealing Monkeys emailed me back and pointed me at another version of Kid Beyond's cover of Wandering Star. I think that's the one I heard, although I didn't notice at the time that it's all a cappella. Thanks PSM!