For me, nothing beats the old Mechwarrior 2 OST. The entire track kicks ass, used to pop the game right into a CD player back in the day.
http://www.youtube.com/watch?v=GM3MwpkVYKQ
OST Track 1 - Umber Wall
http://www.youtube.com/watch?v=aboOgJSkrrw&feature=related
OST Track 2 - Silent Thunder/ Rust Heart
http://www.youtube.com/watch?v=gX4G1RJYTi8&feature=related
OST Track 11 - Pyre Light (my personal favorite)
ah, the memories