Gaming Background Music

Normal Fight/Skirmish

Boarding a ship, a fight with trolls, skirmishes, meant for increasing energy.

Skirmish (Midnight Syndicate) - Has a few sounds of swords clashing.
Deep Trouble (Midnight Syndicate) - Darker feel
How Strange (Midnight Syndicate)
All Drums go to Hell (Two Steps from Hell) - Focus on Drums, over an hour.
Order Battles (The Witcher)
Last Battle (Ocarina of Time, ZREO)
Fuse (Xenogears)
Awakening (Xenogears)
Grahf Emperor of Darkness (Xenogears)
Skyworld (Two Steps from Hell) - Positive and inspirational
The Fire Dragon (The 13th Warrior)
Stalwarts Unite (Fire Emblem:RD)
Fire Emblem: Radiant Dawn Soundtrack - An hour and a half of a mix of great stuff

Epic Fight/Boss Fight

The epic conclusion, last hope of humanity, facing the god of death, meant for really increasing energy!

Lair of the Great Worm (Midnight Syndicate) - A bit of chanting midway through.
Final Confrontation (Midnight Syndicate) - Swords clashing and battle cries halfway through.
Poseidon's Wrath (God of War III)
War (Avatar/James Horner)
Black Blade (Two Steps from Hell)
Moving Mountains (Two Steps from Hell)
To Glory (Two Steps from Hell) - More positive
Archangel (Two Steps from Hell)
Epic10 (The Prime Cronus) - A mix of epic songs with darker and lighter tones

Mystical

Abandoned ruins, ancient cities, strange artifacts, cliff top temples, meant for evoking wonder.

Prelude (Midnight Syndicate)
Eternal Mystery (Midnight Syndicate)
Relic Uncovered (Midnight Syndicate) - Angelic choir feel
Ancient Temple (Midnight Syndicate) - Darker, more mysterious.
The Dike (The Witcher)
Dead City (The Witcher)
Garden of God (Chrono Cross)
The Bioluminescence of the Night (Avatar/James Horner)

Mysterious

Dark places, unknown horrors, strange events, creepy dungeons, meant for evoking tension.

Craft of the Wizard (Midnight Syndicate)
Fens of Sargath (Midnight Syndicate) - Has natural sounds, best used outdoors.
Stealth and Cunning (Midnight Syndicate)
Craft of the Wizard (Midnight Syndicate) - A little chanting mid-way through.
The Secret Chamber (Midnight Syndicate)
The Runis of Bone Hill (Midnight Syndicate) - More positive.

Tower of the Gods (Wind Waker, ZREO)
Lost Child of Time (Chrono Cross)
Going Down (Erdenstern)

Dungeon Crawling/Dark Set Up

Enemy armies marching, dragons far the the east, exploring dangerous places, lost in dangerous tombs, meant for evoking fear.

Troubled Times (Midnight Syndicate)
Decent into depths (Midnight Syndicate)
Beast of the Borderlands (Midnight Syndicate)
The Army of the Dead (Midnight Syndicate) - Some crinkly sounds, bones.
Stone Tower Temple (Majora's Mask)
Dungeon Music Compilation One and Two - A bit more relaxing.
Evil Overlord (Erdenstern) - Choir, evil, could be used for combat.
Dracula Soundtrack (Bram Stoker's Dracula) - Playlist, mix of energetic and calming, all dark.
The Dune Soundtrack - Darker, 1+ hour song, can mostly be used for Dungeon crawl.

Normal Travel/General Ambience

Overland travel, movement, arrivals, meant for evoking general ambience.

Ride to Destiny (Midnight Syndicate) - A bit on the darker and tenser side.
Forest of the Black Moon (Xenogears)
Emotions (Xenogears) - Very positive, but active
Overworld (Terranigma) - MIDI sounding.
Gothic 2 Soundtrack - 1.5 hours, subdued and dark.
The Celestial Aeon Project - A range of mostly chill songs.
Reel Around the Sun (Bill Whelan)

Epic Travel

Cresting the Mountain Ridge, first time on the road, last time on the road, setting sail, meant for evoking inspiration.

City of Sails (Midnight Syndicate)
Leftovers From Dreams of the Strong (Xenogears)
The Blue Traveler (Xenogears)
Wings (Xenogears)
Iknimaya - The Path to Heaven (Avatar/James Horner)
Jake's First Flight (Avatar/James Horner) - Has peaks and valleys.
New Beginnings (Audiomachine)
Ice of Phoenix (Audiomachine) - A bit uneven in tone though, peaks and valleys
Epilogue, Into the Green (Erdenstern)
Quest for Glory (Soul Calibur II)

Town/Inn

Relaxed evening at home, sitting around the campfire, sleepy little town, relaxed city square, meant for evoking calm and reflection.

Peaceful Moments (The Witcher)
Dusk of a Northern Kingdom (The Witcher)
RPG Chillout Music - A dozen hours of calm, pleasant atmospheric music.  Playlist.

Lively Tavern/Busting City

Crowded market, drinking songs, arrival in an exotic city, banners streaming from towers, meant for evoking interest and excitement.

Deku Palace (Majora's Mask, ZREO) - Slight middle eastern theme
Outset Island (Wind Waker, ZREO) - A bit more calm
Dazil, City of Burning Sand (Xenogears) - Strong middle eastern theme.
Solaris, Eden of Heaven (Xenogears)
RPG Tavern Music Compilations One, Two, Three, Four
Samai Al Salam (Salim Al Nur) - Extremely strong middle eastern theme
Taverns (Baldur's Gate)

Varied

Longer and more varied songs, used in the background over extended periods.

Nemisis (Two steps from Hell) - Hour+ playlist, mix of lighter and darker tracks but all energetic.  Can use broadly for battle.

Invincible (Two Steps from Hell) - 1 hour song, lots of epic mildly positive.  Can use broadly for epic travel or battle.
Conan the Barbarian, Full Soundtrack - 1 hour song, mix, starts of with some narration.
Assassin's Creed 2, Full Soundtrack - 2 hour song
The Last Temptation of Christ - 1 hour
Vagrant Story OST - 2+ hour playlist.
Epic Weekly (The Prime Cronus) - Very long playlist with mostly epics, both positive and negative.
The Braveheart Soundtrack - 2+ hour song.
Gladiator Soundtrack - 2 hour song, generally high energy.
Best of Inception - 45 Minutes, generally darker high energy.

No Music, Just Ambience

10 Minutes of Pirate Ship Sounds

Nobilia Marketplace (Secret of Evermore) - No music, just background crowd noises.

Other Compilations

Planet Rust and The Perfect Raid Audio

Feel free to post more in the comments!