Rondellus are a Renaissance/early music group from Estonia who in 2003 recorded Sabbatum, an album of Black Sabbath covers performed in a medieval style, using instruments such as the lute, harp, hurdy-gurdy, psaltery and frame drum, and sung entirely in Latin... The result is a thing of transcendent beauty dominated by vaulting Gregorian-chant-style vocals that one would never associate with Ozzy Osborne and co. Samples of these angelic renderings of the Sabbath's work are available from the album's website. (The album itself can be purchased through CD Baby.)
(Footnote: Sabbatum actually won best classical CD at the 2003 Estonian Music Awards... Pretty damn enlightened people, these Estonians!)
If you like the idea of high concept reworkings of metal standards but prefer something that actually rocks, then check out Japanese vocalist Dokaka... When the bassplayer in the band he drummed for failed to turn up for a practice, Dokaka tried humming his basslines and turned out to be so good that the band's singer suggested he do a professional recording. Dokaka took up the challenge and applied his talents to other instruments; ultimately producing entirely acapella versions of songs by Metallica, Nirvana, Iron Maiden and even Stevie Wonder.
He posted these recordings on the IUMA website and, in no time at all, he was a star with offers of gigs as far afield as Seattle. Now, he's moved to a dedicated domain and the latest news is that he's just finished recording with Bjork.
For the final portion of this segment, we turn to the strange and frightening world of Norwegian black metal... With their heyday of church burnings and murder trials behind them, some members of this satanic doom-core fraternity have decided that it is time to "mature" musically. This has meant embracing techno-pop and becoming as "unmetal" as possible...
The result is a genre which has become known as "lounge-core". The foremost exponents of this not-really-metal-anymore music are Beyond Dawn, who sound like Depeche Mode on lithium. (Their latest, and most lounge-core album, Frysh, is available from Aquarius Records. Here's an mp3 off it called Righteous Underground.)