Schadenfroh - you should really pick up a copy of Exult and "borrow" Ultima 7 parts 1 and 2... Ultima 8 would be nice to play if it would actually run on Windows.
To be honestly, the list SHOULD go something like:
1. Ultima SERIES. We're not talking UO, we're talking all of Ultima. It spanned several computer systems and technology bases, and evolved just as gaming did. Starting with the text based Ultimas, which spawned or was spawned by MUDs. The natural progression to Ultima 7 which was the first realtime persistant world there was. EVERYTHING in Ultima 7 happened all over the world, not just as responses to triggers to a player event. Ultima 8 was a refinement of this, and Ultima 9 was (unfortunately) a failed attempt at translating this into 3D. Ultima Online took everything that was Ultima 7, and everything that was MUD, and put it into the first realtime graphical multiplayer roleplaying environment which still stands today.
2. Diablo Series. This type of fast action RPG had less RPG elements than button mashing, which has pervaded almost all current MMO interface strategies to date.
3. Everquest. EQ would be the first and most successful POPULAR 3D MMORPG, taking all that made UO popular, and putting in the first 1st/3rd Person control.
4. Final Fantasy Series. This took the Ultima formula, and brought it to the console world.
5. Planetside. Not the first, but the first commercially viable MMOFPS with RPG elements. (Looking forward to Tabula Rasa to enhance upon this)
I would ONLY note World of Warcraft because they have taken the tried and true formula, combined it with a HUGELY popular worldwide franchise, spent the time, money and effort to polish it to their high quality standards and put it out there. Blizzard really has done NOTHING new with World of Warcraft that wasn't already done in EverQuest. They simply executed a well designed product with the backing of a huge franchise much better than anyone else to date.