This one time...
My last campaign ended with civil war. The mercenary company employing the pcs launched a coup against the religious government of the city, and the slaves in the slums rioted en masse. The last encounter was the PCs facing down the Temple Guard (elite goblin fighter/rogues with spiked chains). Several rounds in, they heard the yelling of the mob. Because, as some of their mercenary work, they had worked as slavedrivers, the mob rushed them and the temple guard indiscriminately.
They had nearly cleaned up the guards, but upon sighting the mob they fled the city. It led to a nice conclusion, as I got to describe the sight of the city blazing behind them. Also, because the campaign started with the characters migrating into the city, there was some good symmetry there. "You've eventually decided that whatever the terrors of the Southlands, they cannot be worse than what you have witnessed in the city of Kreyak."
Anyway. In the last encounter I put a short playlist on loop. You can probably see my thinking behind it:
Burnin' and a Looting (Bob Marley)
I predict a riot (Kaiser Chiefs)
White Riot (The Clash)
And one or two others. There may even have been a Woody Guthrie track on that one.
Anyway, it wasn't terribly atmospheric, being a rather varied list, more lyrical than melodic. I think I'll try music again in my next campaign. I'll stick to a subtler score though. Probably some classical music, with a few picked out for bad guys. What I'd really love to be able to do is cue just a snippet of music from a villain's theme when they discover evidence of his work, find his secret hide-out, et cetera. But I don't think I have the technical wherewithal to pull it off right. (Nor do I want to take the time to install or learn new software).