These are main MMOG for 2005, maybe some of them won't be released on time. But we will ba able to play some expansions of existing games this year, which will add new contensta nd improve game.

Anarchy Online. Alien Invasion has been a fresh air blow for Anarchy Online, changing its contents and improving gaming experience.
Dark Age of Camelot. Catacombs has remodeled DAoC graphics thanks to DirectX 9.x and added a new subterranean world waiting players to explore it.
Starwars Galaxies. Jump to the Lightspeed has added a new game mode, spacial simulation, where rebels and Empire have great spaceships battles.
Shadowbane. Throne of Oblivion has added new territories and better alliance and war system, apart from a new vampire race.

Many games won't have expansions but free updates.  And even some developers like NCSoft has released 2 free adons for Lineage 2 and 3 for City of Heroes, or Playnet Inc. which has released a new addon for World War II Online adding airborne troops. So 2005 seems to be a great promising year for MMOG.