"Isotoxin", by Necros (Andrew Sega), (who also provided a song for Unreal Tournament, see below) a song borrowed from an obscure gamenote In Pursuit of Greed, its intro in fact is featured in the level Outpost 3J.
The darkly evocative Vortex Rikerstheme, which perfectly suits the ghost ship it accompanies.
"Dusk Horizon", the first track you hear upon stepping out into an alien world. Sounds even better when combined with the natural chirps and bird cries of Nyleve's Falls.
The industrial-sounding "Dig (Shareware version)" that plays in the Rrajigar Mine levels has 3 great sections; the progressive, upbeat main theme is complemented by a threatening minor key intro (starts at 4:34) and a truly awesome action track (2:40 - 4:33).
Appropriately enough, the Ending Theme has to be the crowning music in a soundtrack full of CMOA; twisting through triumph, sadness and suspense about what the sequel will hold, it ends the game in epic style.
Even the Expansion Pack, Return To Na Pali, has a great Intro song. Of course, made by both Brandon and Van Den Bos.
"Twilight Horizon", an extended remix of Dusk Horizon from the previous game that accompanies the first level, is also great.
Go Down, the iconic track of two of the most iconic Unreal deathmatch maps ever: DM-Deck16][ and DM-HyperBlast. Both those maps and the song itself became classics for the remainder of the series, and for MANY good reasons.
Foregone Destruction, the iconic song of the most iconic Unreal CTF map ever, Facing Worlds. Like the Deck maps mentioned above, Facing Worlds is a Crowning Level Of Awesome and one of the hallmarks of its gameplay mode (Capture the Flag). Part of that is the level design. Part of it is the jawdropping milieu. And part of it is this music.
Then listen to this remix by dj Frakture and melt from the concentrated awesomeness. He also did remixes for Botpack#9 (DM-Phobos) and Skyward Fire (CTF-LavaGiant, AS-Mazon).
In Unreal Championship, the port of Unreal Tournament 2003, the music duties fell to Starsky Partridge.note The songs are those starting with "Level" Several of the songs in there were later ported to Unreal Tournament 2004:
For a further proof, and a much more muted song than "Go Down" which borders on Soundtrack Dissonance, check out the simply named Level8 from UT2003/UT2004, the theme of the Tokara Forest stage.
The main theme of Unreal Tournament 2003, even with the game falling into Canon Discontinuity, and which you can also find in Unreal Tournament 2004. The most epic intro for any of the Unreal games. It gives you the sensation of fighting a gladiator game.
The menu theme of UT2004 remixes and expands the '99 version - all on a full orchestra!
If you liked "Save Me", then listen to UT2004's MK-ish DM1.
The techno-orchestral remix of "Go Down", called Hyperblast Redux, is even more awesome than its counterparts from the other two games it was featured.