The info below confirms some new instances, giving us even more opportunities and reasons to learn big raid skills. (Info taken from WoW.net site)

THE GATES OF AHN'QIRAJ INFORMATION (PATCH 1.9)

14 November 2005 - A great evil is lying in wait in Silithus, ever patient, ever enduring. Mortal hands are at work awakening an ancient menace that, once set lose, will shake the very foundations of this world. Evil is stirring where mortals were never meant to tread. The world is waiting for a champion to step forward and stop the coming darkness before it is too late.

One of the main features of this content patch will be the unveiling of Ahn'Qiraj, an instance in Silithus that will feature a 40 man raid group and a "more casual" 20 man raid group. Please find further information below:

* The Ahn'Qiraj area is opened up by opening the gates of Silithus located at the Scarab Wall in south Silithus – a structure of truly cyclopean proportions. This will actually be a one-time world event that can be triggered only once per server and it requires the help of everyone on a server to open the gates (both Horde and Alliance). Once the gates have been opened on a server, that server can no longer participate in the gate-opening event.
* Once opened, adventurers can enter two new raid instances, one is a 40 man raid group and the other is a 20 man raid group, the 20 man raid group (The Ruins of Ahn'Qiraj) will allow "casual" players to experience new raid content. The 40 man raid group (Temple of Ahn'Qiraj) is said to be slightly harder than Molten Core. Players will also be able to obtain special Silithid mounts that can only be used in the 40 man raid instance.
* Most notable about Ahn'Qiraj is the fact that Qiraji have enslaved the Silithid bugs that players have become familiar with encountering around the continent of Kalimdor. The Qiraji are in fact being directed by some unknown power. It is unclear what this power is, but it is clear that the Qiraji are evil and their intentions remain a mystery, though the Qiraji and their enslaved Silithid minions are obviously hostile to all other residents of Azeroth and what they are up to is essentially "not good."
* Mobs that look like the Egyptian god "Anubis" is called "Anubisath X", where X is their job or specification.
* The Twin Emperors of Ahn'Qiraj are named Vek'nilash and Vek'lor -- they're the two end bosses in the 40 man.
* The Prophet who is found in the very beginning of the instance is called Skeram. (see first encounter and prophet screenshot).
* The final boss of the 20 man raid is the blue horrendous looking creature.