Can't think of many in my tired hungover state right now. Will try to get back to this. I don't know if I liked it so much cos I was quite stoned, but I remember enjoying Very Bad Things .
Its about a young man who is obsessed with death and keeps pretending to commit suicide in increasingly bizarre ways. In the meantime his mother is desperate to get him married off and brings girls home to introduce him to. He goes to funerals and meets a very old woman and they fall in love and, well anyway, it is absolutely hysterical. I saw it at the pictures in my teens and it was brilliant
Heathers yes until the last 20 mins - when you see the extras on the special edition with the originally planned ending what they did is a total kop out.
My all time favourite dark comedy is Dr Strangelove. It is an anti war film from the 1960s. Peter Sellers plays three different roles in it. If you have never seen it make sure you watch it sometime. If you have already seen it, watch it again.
I also like Fargo which has already had a few mentions.
I loved the book, but felt the film lost a lot of the humour, seemed a bit of a messy translation (kinda like Dune and the Hitchhikers guide debacles).
To be fair, it was a more or less impossible book to translate onto screen, I think they did about the best they could. They got most of the madness and the contradictions into the script.