https://www.youtube.com/watch?v=ec0XKhAHR5I
This one is kinda like The Warrior Song, fitting the whole "marine pride" theme, plus it's one of the most known Vietnam war era songs; the Aliens film was heavily influenced by Vietnam, so this would make sense. I know it's 2:21 minutes long and the lobby lasts three, but I think forty seconds of silence isn't that unbearable.
https://www.youtube.com/watch?v=1ErIJuYFh1A
It's from the Aliens film, it's almost exactly three minutes long, and it fits the whole CM feel completely. There's also a new version from the Colonial Marines game if a faster and more modern version is prefered.
https://www.youtube.com/watch?v=QSk1Usj_7Ug
I know this differs from the whole "marine badassness" song, but it is simply so eerie, creepy and atmospheric that it definitely deserves a spot. The ambience it gives reflects the sheer threat never found before by the marines, but that they will surely have to face down on the planet. Also even though the video is 3:18 long, the song itself ends more or less at 3:01. Finally, it's from an Alien game too!
https://www.youtube.com/watch?v=7KYgGFKnHNw
Same as above.
EDIT:
https://www.youtube.com/watch?v=EVWESrIt3uk
I also found this. It's 2:35, leaving 25 seconds of lobby silence. It's just an idea tbh, if you need an extra song to show the Predators some love as well.