As of yet, I haven't found any mods like this for 1.3.1, so here goes...
Pretty simple: there is a way to rearrange pieces of background music, i.e. you can delete an unwanted song from the Minecraft ingame soundtrack and/or add music to the ingame soundtrack (In Search of Diamonds FTW!). And one last thing: it could set triggers to play music:
on new world;
at title menu;
on hardcore death;
on mob pathfind (battle music).
Feel free to overlook this, but I know at least a couple of Minecrafters who would find this cool!