I figure since there's a saysounds suggestion thread there might as well be a loading music suggestion thread.
If you're not sure what loading music is: it's a feature (that you can enable with the !loadingmusic command) that will play random music while you're loading into the server during a map change. Everyone who has the feature enabled will hear the same song during a map change.
You can check out what existing music is available
here.
So feel free to use this thread to suggest what music should be added!