I was already thoroughly enjoying Alien Swarm by playing it the way that the developers intended it to be played, music and all. Soon enough though, my roommate pointed out to me that there was an option in-game to choose your own battle music. I was immediately blown away that they would include something like this in the game. I hadn't bothered to go digging around in the audio options menu, so I probably wouldn't have found it at all, or at least not any time soon. At the time of this discovery, I had yet to complete the Jacob's Rest campaign, so I wanted the music I was going to add to contribute significantly to the overall atmosphere of the game. Not wanting to go through too much effort, I decided to go digging around in some of the video game soundtracks I already had on my computer and add some grim, ominous songs to create some more tension. What I have listed below is what I currently have in the game.
 

Track Listing

I was already thoroughly enjoying Alien Swarm by playing it the way that the developers intended it to be played, music and all. Soon enough though, my roommate pointed out to me that there was an option in-game to choose your own battle music. I was immediately blown away that they would include something like this in the game. I hadn't bothered to go digging around in the audio options menu, so I probably wouldn't have found it at all, or at least not any time soon. At the time of this discovery, I had yet to complete the Jacob's Rest campaign, so I wanted the music I was going to add to contribute significantly to the overall atmosphere of the game. Not wanting to go through too much effort, I decided to go digging around in some of the video game soundtracks I already had on my computer and add some grim, ominous songs to create some more tension. What I have listed below is what I currently have in the game.
 

Track Listing

This is a pretty cool feature. I use Blotted Science - Night Terror right now. Being an instrumental track and pretty alien sounding, it's perfect for Alien Swarm. It starts off creepy so you know something bad is about to happen, and then unleashes the chaos (while continuing to be creepy throughout).

 

  How could you use anything else?

Dammit, I still can't get the music thing to work. Can someone please explain it to me? It's like I add the music, but it doesn't ever activate, even in offline practice. What gives?

" Dammit, I still can't get the music thing to work. Can someone please explain it to me? It's like I add the music, but it doesn't ever activate, even in offline practice. What gives? "

I prefer this: 
 

Queen - Under Pressure
Dragonforce - Through the Fire and Flames
Metallica - Enter Sandman
Metallica - Frantic (Fits the most in my opinion.)
Foo Fighters - Pretender
 
@Chuggsy:
You just blew my mind!
Right click to GALACTIC PUNT.

I use this:
 
 

" @ThePwnee said:

" Dammit, I still can't get the music thing to work. Can someone please explain it to me? It's like I add the music, but it doesn't ever activate, even in offline practice. What gives? "

I had the same problem for a long time, and then one day it just started working. I tried posting about it on the Steam forums, but nobody bothered to reply or help out. My best advice is to just give it time I suppose. It's a weird glitch that I'm not sure there is actually a solution for yet. "

not to sound like a metal elitist but i find Metal to be the best actiony music, especially for such a movie-action oriented game (all the bullet time sequences n stuff) 
 
I wont recommend anything, but i think the first band to come to mind is Rage Against the Machine.. thats why they used their music for The Matrix movies

I've tried a bunch of different songs from different genres, but for some reason or another, Two Tribes by Frankie Goes to Hollywood is perhaps the most amusing fit while still being vaguely appropriate.

I use some of The Black Mages battle music remixes, but now I have some new stuff to put in thanks to this thread (Starship Troopers and P4... I don't know why I didn't think of those.).
 
Edit: These are the two I use at the moment.