Dear the Spiral Knights Sound Guys
You guys are amazing. When is the soundtrack going to be released? I neeeeed it so badly!
Music is generally the worst-done part of an MMO, but Spiral Knights' sound has so much love and awesome put into it.. You guys deserve a medal or something. I salute you!

You can find the in-game music as .ogg files in the following folder (Win7):
C:\Users\USERNAME\AppData\Roaming\Three Rings Design\Spiral Knights\rsrc\sound\music
There's about 40 tracks, mostly the ambient level music, and a few little fanfare clips like when you complete a level or arena.
Aha! Thanks, majic. Though after a while of searching it turned out mine was hiding in AppData\LocalLow\spiral
Computers. >_<
It's in different folders depending on how you installed it and what OS you have -.-. Check the program folders or the Application Data folders.

In windows XP, you can find the music at C:\Documents and Settings\[user_name]\Application Data\spiral\rsrc\sound\music
MMO's usually have good music, especially asian themed ones. Though I do have to agree that spiral knights instantly impressed me in the audio deraprment. It was better than anything i heard before. The game needs more of it. My favourite music is from jigsaw valley. Game needs more of that melodic mellow stuff in the dungeons :3