Unfortunately, I've had difficulty finding appropriate music for Battletech.
While most modern PC games end up playing same-old military marches, I really like the soundtracks to Mechwarrior 2, and subsequently, Mechwarrior 2 Mercenaries.
MW2 has an excellent soundtrack that, although no actual instruments are used, convey a universe that toes the line between familiar and alien, while at the same time, not coming off at tacky techno music. The closest I'd ever come to it was stuff like YatKha, in terms of giving a classical-but-electronic, familiar but alien sentiment. I almost want to say that in many cases, the music feels somewhat tribal, as well. It honestly fits in perfectly with the Clans.
http://www.youtube.com/watch?v=gX4G1RJYTi8
While Mechwarrior 2 Mercenaries had a similar feeling, there was less of a tribal atmosphere about the music, and less attempts to make it sound like classical music, more playing into the grim, merciless universe of the 3040s' inner sphere, ranging from ghostly classical sounds to fast-paced techno-laced metal riffs.
http://www.youtube.com/watch?v=OgsjIXaJTWI