I don't know if i'd call Halo or Unreal Tournament MMO's per say, cause then i'd have to call out on:
Warcraft III
Starcraft,
Generals,
Battlefield 1942, 2, 2142,
etc. etc. Any game that has an online lobby.
Heh, The proper definition of an MMO usallay means you have a MASS of players playing on the same server The games where you are limited to 8, 12, 16, 24, 32 and 64 don't really count. MMO stands for: MASSIVE Multiplay online. So you'd want games where you join thats theres at least potential to have 100 people playing in the same enviroment at the same time. The games listed above along with halo and most other FPS are really what should be called Multiplay lobby games. WoW, Mu, Eve, RO, even silly little runescape are what mmo's are A large number of people join an enviroment and work in the same enviroment at the same time, usally the enviroment is continual even when your not there it continues. Another MMO would be Cybernations, or Utopia by swirve though Browser based there more mmo than Halo and unreal. Thats my two cents. heh.
Earth 2025:
http://games.swirve.com/earth/ <--- Modern based, Building a nation with nukes tanks, turrets etc.
Utopia:
http://games.swirve.com/utopia/ <--- Fantasy realm based, Nation building with Wizards, thieves, elve's, orcs etc. etc.
Cybernations:
http://www.cybernations.net/ <--- This is a pretty complex one, from religion to tax rates, Alliances, Goverment, military infistructure, happiness of your populus etc, You have to juggle alotta cakes for this one!
Those are just three strategy based MMO's that i know of, There was a FPS MMO I can't recall the name of it off the top of my head though. heh, I don't think it did too well from memory or it mighta got canned.