I've not had music in the background for a D&D session (yet). There are a few things I would like to try / experience, for serious or for fun.
The enemies are chasing us: William Tell Overture (also known as the Lone Ranger theme)
Entering the sepulchure of the Legendary Artifact: Siegfried's Funeral March (from Wagner's Ring cycle)
Activating said artifact: Thus Sprach Zarathustra (2001)
BBEG's enforcer lieutenant arrives to fight the PCs: Duel of the Fates (Darth Maul confrontation)
BBEG himself arrives: Imperial March, from Star Wars
PC tries some spectacular physical stunt and rolls a 20: Indiana Jones theme
Final Victory: Siegfried and Brunehilda in the Forest (Wagner's Ring again)
While those CAN work and do work, I have noticed that having immediately recognizable songs can often distract players and make them think about something other than the adventure they're playing. I like to use more obscure movies, or movies you've surely heard of, but the music soundtrack wouldn't be the first thing that comes to mind. A few I've sampled over the years include:
Alien, Aliens (mostly the action scenes), Slither, Ravenous, Blade, Abominable (as in the snowman), The Omen, Jupiter Ascending, and many more.
Game soundtracks are good too, but usually only recognizable if someone played the games. I've used Halo, Gears of War, Quake, The Longest Journey, Half Life, Doom, and others for mood music. The game soundtracks tend to be far less distracting than playing, say, the Star Wars theme song.