I don't care to count how much money I've burned on online gaming over the past decade or so.
Lets see here...
Aces High 1 + 2
Star wars Galaxies
A Tale in the Desert I, II, III, and early IV. (Awsome game

)
Vanguard
LOTR Online
WoW
Warhammer Online (only very briefly)
Eve (briefly)
Navy Field
Not quite MMOs, but still multiplayer:
Starcraft
Counter-strike
Day of Defeat
COD, old school

BF 1942 (still one of the most fun, especially 12v12 clan fights)
Freespace
Diablo series
Warcraft series (war 2 battle.net edition for the win

)
A few others that I'm missing off the top of my head at the moment...