1. World of Warcraft.
From 2004 to 2012 WOW made around 8 billion dollars (that's MORE than double the Avatar and Titanic movies combined).
2. Warcraft 3
Reason: It was not only the most played RTS for a long time (even till today) BUT it ALSO spawned a whole new PC genre as such: the DOTA game play and even at your number 25 you find a game that is completely based on the engine, the maps, arch heroes of Warcraft 3 and that's League of Legends... which just happens to be the most played PC game on Xfire at the moment.
Without Warcraft's 3 engine, map editor and initial Blizzard programming tools there would not even be a League of Legends or Dota like game at all.