Musical scores in video games, like in movies, set the emotional tone for the action. The Internet Archive has a wide range of music you can use in your games. Be sure to check the terms of the license before you use an audio clip to determine if your use matches the license. Some clips are in the public domain, others are licensed under Creative Commons terms of varying restrictiveness. Read the license before you use the clip.
The following clips are from a gem of a collection by Torley Wong, who released 230 audio clips to the Internet Archive under a Creative Commons Attribution ShareAlike 3.0. You can use the clips for any purpose, including commercial, as long as you credit the composer.