Diablo III has officially been announced at the Blizzard invitational in Paris today. It will be released for PC & Mac.
No release date has been given, but that's no surprise with Blizz games.
The official Diablo III site is now up and running and you can find it here
http://eu.blizzard.com/diablo3/
Includes both cinematic and gameplay trailers as well as more info.