During one of the dozens of Starcraft II panels from Blizzcon, they had a number of the voice actors on stage. One of them was 
Michael Gough, the actors who voices Deckard Cain, and he promptly launched into his most famous voice, with some Diablo quotes, jokes and a bit of the Deckard Cain rap. There’s nothing D3-related, but it’s cool to stay a while and listen while watching the real person do that thousand year old voice.
Michael Gough speaks at the start of this video, and adds a bit more at the end of a second video. Click through for that embed, plus a short video of Michael Gough giving a fan a short greeting in his most famous voice.. Thanks to Fmulder for the tip.
Part Two from the Starcraft voice actors panel.
Bonus very short video of Michael Gough giving a fan a personal greeting, in Deckard Cain’s voice.