Either SACD or DVD-Audio depending on which company you ask ;)

http://www.cdfreaks.com/article/95

http://www.digitalaudioguide.com/faq.../faq_intro.htm

SACD is around today, but there's not been a huge takeup, DV-Audio is still up in there as far as I know. Seeing as CDs are good enough for most people I'm not sure there'll be a huge uptake, especially with the advent of electronic music distribution.