Late this afternoon, Blizzard created an official forum for their next expansion, The Wrath of the Lich King. Both the U.S. Wrath forum and the European Wrath forum are just now filling up with the usual questions, and some are already getting blue responses.
From the U.S. forums:
CM Nethaera confirms one new hero class is planned for each expansion
CM Bornakk confirms the level restriction on using flying mounts in Northrend has not be set yet (maybe L78, maybe not)
CM Bornakk implies that initial travel to Northrend will by boat and zeppelin
The European forums have plenty to offer as well:
CM Vaneras has moved the all things announced about Northrend post to this forum and confirmed today that Ulduar is a dwarven instance that will be accessible by both Horde and Alliance
CM Vaneras also moved the all things announced about Death Knights post to this forum
Forum VIP Schwick has stickied his round up of all confirmed dev quotes about the Wrath expansion and put it at the top of the forum
Keep your eyes on those forums and on WoW Insider for future news about the expansion.