Warcraft I: Orcish Victory Music, especially when the massive Orc Chieftain's portrait is splayed in the background. Not to mention the Orcish narrator explaining the utter destruction of the Kingdom of Azeroth.
Warcraft II: It's called simply Human 1, but the name is the only non-epic thing about it.
Orc 1. War drums playing? Rally the grunts, it's time to go to work.
Orc 3 uses a minute and a half to build up the single greatest harpsichord face melter in video game history.
Although there is unfortunately no Youtube video of either theme, the "Comradeship" and "Blood Elf" themes are fantastic. For one that there is, see Arthas' Theme.
A link to 'Comradeship. The 'Vengeance of the Blood Elves' theme is the second.
From the Frozen Throne expansion, "Human 4," which sums up the state of the Alliance perfectly.
World of Warcraft has the dubious distinction of creating music so epic that it took years for the developers to find a place in the game worthy of it: The Shaping of the World.
They learned their lesson in the Burning Crusade expansion, and had a specific quest in mind when writing Lament of the Highborne.
The music that plays in ShadowfangKeep is pretty darn awesome.
The music in Arcanist Doan's room in the Scarlet Monastery. It plays elsewhere as well (including one place in the Molten Core). It's the last few seconds of a track called "Legacy" from the main game's OST (the rest of the piece isn't used).
Some of the Burning Crusade's ambient music is subdued but spectacular, be it the haunting swells of organs and strings in Terokkar Forest, or the ominous chants of Shadowmoon Valley.
The music for Shalandis Isle took new Blood Elf players by surprise, but in a very good way. It was so popular that Blizzard has since stuck it in Night Elf inns and the Temple of the Moon in Darnassus (possibly providing the first reason to hang around the city).
A Call to Arms doesn't appear very often, but you've gotta love the epicness of the second half. And the nice lead-in from the first.
An upgraded version of it appears in the Wrath of the Lich Kinglog-in music.
The distinctive leitmotif of Illidan Stormrage, found inside the Black Temple and in various places across Outland. (Unfortunately, the best examples can only be heard by going into the game's .mpq files.) A melody of ominous strings and bitter reed instruments.
And then, there is Arthas, My Son, that song playing behind the incredible intro cinematic for WOTLK.
Or the more militarized Assault On New Avalon arrangement that serves as the Death Knight theme.
Silvermoon City is the only city to have separate music for day and night (note that the first two minutes on those videos are the same, being the theme that plays in Falconwing Square regardless of the time of day). It's so awesome it made it into the title theme for both expansions!
Another beautiful piece of Northrend music can be found in the found in the Grizzly Hills, a gorgeous redwood forest with a distinct old American Midwest vibe, complete with lumberjacks, trappers, beavers, grizzly bears, and Native Americans-erm, trolls.
The foreboding and gloomy theme of the Un'Goro Crater and the Swamp of Sorrows is great, but the Sholazar Basin theme is also good. Another theme that fits the zone is the Burning Steppes theme: you can almost feel the heat. Unfortunately, the theme for the Battle of Mount Hyjal was not used in the raid instance itself. Fortunately, the Karazhan theme did eventually appear in the game.
The Joust music, new to the game from Patch 3.1, is also pretty amazing.
The latest background music to the Trial of the Champion/Crusader instance is incredible at setting the tone of the instance. It's a lot more noticeable than the music in many other dungeons.
And now the Cataclysm Main Theme has been put up on Youtube. Contains pieces of previous themes and zones.
The theme for Stormwind definitely catches the heroic, righteous nature of the alliance. Listen to it here.
The Night Elves get a new theme in Cataclysm, and it is incredible.
The new Orgrimmar themefor Cataclysm is the perfect representation of the Horde.
And a new entry into the rolls of music tracks that really shouldn't be bad guy themes, Breath of Al'Akir is the sweeping theme of Skywall. Sadly, the main place players will hear this piece is the Vortex Pinnacle.
Patch 4.3 released this awesomeness. It almost becomes Autobots, Rock Out! in some places, but it's done so incredibly well that you truly feel like you're fighting against a force that seeks to annihilate the entire world.
The music from Mists of Pandaria gives off an Asian vibe while remaining true to Warcraft. And it is awesome.
