Gee, happened to me once. My neighbours threw in a party at 10pm on... a Sunday. I was to be up at 5 am the day after (to go to school, teach, and be assessed) and two of my housemates were to be up at 6 (trainee nurses, learning how to get blood samples, no further details needed I guess).
We called the police at 2am after going to the neighbours' FOUR times, and the police wouldn't turn up. Said we had to complain by the City Council and... neighbours might get their stereo equipment confiscated!
I ended up calling their landlord the day after (whom happened to be ours too), and I don't know what he said to them but that proved REALLY efficient...