The MechWarrior 2soundtrack. It's probably among the most memorable video game soundtracks ever. It makes even the most mundane activity in the game seem epic. Even listening to them outside the game, they sound like they should be played while something epic happens. The soundtrack was composed by both Gregory Alper and Jeehun Hwang, the latter of which went on to compose the similar sounding Battlezone soundtrack.
Ghost Bear's Legacy continues this trend. Track 11 in the Battlepack Edition. Notably that edition's soundtrack was composed by Carey Chico who, you guessed it, was also involved in Battlezone's music but in the sequel.
The third game didn't have much of a soundtrack due to its long and troubled production but it was when Duane Decker took over for the series' music (and both MechCommander games), giving us two tracks to show what was to come, first being the main theme that plays on the menu and every even-numbered mission and "The Block Is Hot", a more Eastern theme and ominous hymning that plays every odd-numbered mission. Pirate's Moon gave us three movements in a single track this time; the first is a climactic theme with tribal drums, the second is more dark sounding and was re-used both in the base game's trailer and epilogue, and the third is faster and more frantic before it ends with a short, climactic ending.
Wednesday 7 from Mechwarrior 4: Vengeance is up there too.
Mechwarrior 4: Mercenaries: Next Movewill get stuck in your head depending on how long you spend in the MechLab.
A New Dawn is an album remix of MechWarrior 2: 31st Century Combat composed by Timothy Seals with remixes of Pyre Light, Silent Thunder, Arkham Bridge, Sable Flame, Umber Wall, Iron Piston, Temper Edge and Golden Spade. They're longer and much more climactic than the original songs.