The videos that are available are hosted on Vimeo, and we've embedded them after the break for easy viewing. You can take a look at footage form Utgarde Keep, Drak'tharon Keep, and The Nexus.
I know that some people are concerned with spoilers, so don't watch these if you don't want to see everything. They're taken from the alpha and the videos give a clear view of everything in the dungeons.
In this video the level 70 dungeon Utgarde Keep is explored. UK, as I'm sure it'll end up being called, is a multi-winged dungeon that has instances for level 70 – 72 players and for level 80 players. Much like today's Hellfire Citadel.
Utgarde Keep was also playable at both BlizzCon '07 and at the recent World Wide Invitational 2008.
In Warcraft lore, Drak'Tharon Keep is where Arthas stayed as he went looking for Frostmourne. The Keep is located in Grizzly Hills. It was originally occupied by Ice Trolls, but has sense been taken over by the Scourge.
Drak'Tharon Keep is for level 74 – 76 players.
The Nexus is another multi-winged dungeon that is for 5-man level 71 – 73 groups, 5-man level 80 groups, and 10/25 man raids (where players will encounter Malygos).