Blizzard has announced the development of Diablo 3 at WWI in France. There is no release date scheduled as of yet, but generally they take approximately 1 to 2 years after announcement. There are some pretty cool videos you should check out on the diablo3 portal site below:

Details (as they emerge and are released) can be found here:
http://www.blizzard.com/diablo3/ or http://www.diablo3.com

and here:
http://www.blizzard.com/wwi08/

Europe members can use this site for possibly faster access:
http://eu.blizzard.com/diablo3/

Yes, we will fully support Diablo III community activities, including discussion and trading. Please drop by the Diablo III discussion forums that have been created:
Diablo III Discussion Forums

We will be adding more sub-forums in the coming months, including trade forums when they become applicable.

Keep on slashing!

--Paul (njaguar)