Diablo 3 will, as rumoured, have a collector's edition. This was confirmed as Blizzard has submitted a video to The British Board of Film Classification labeled "Diablo III Video Game Collector's DVD".
The Diablo development team have been asked about a Collector's Edition a number of times, but have declined to give out any details. At a crafting sanctuary panel at BlizzCon 2010, a fan asked what exclusive stuff would appear in the collector's edition, and was answered with "we haven't talked about it all yet. But something cool, I'm sure".
The Collector's Edition for StarCraft 2 was released at the same day a the regular game.
Links
Diablounderground.com - Source
BBFC.co.uk - The British Board of Film Classification