A new format of CD packaging made of card, "digipak editions" of CDs usually have extra tracks and are limited edition.
> "Muse - Hullabaloo: Digipak edition"
> "Slipknot - Slipknot: Digipak edition"
> "Anathema - The Silent Enigma: Digipak edition"
> (thats all the ones I've got but there are loads!)