Halo is an obvious favorite. That music really gets you in the mood for some epic action. Plus it is very recognizable. Whenever I hear it I just want to go and have some epic battles in a scorpion.
The CoD franchise also has good music though. I like it because it has a mix. The old WWII music, while cheesy, is still fairly patriotic and emotional. The new music, however, just gets me pumped. It's loud, epic, and perfect for an action game. I'm the kind of person who judges music by how it makes me feel, so CoD always gets high marks.
I know other games might have "better" music but these two just get me excited every time I hear their soundtracks.