It's great when Producers/Directors understand how much a good closing credits song can enhance the atmosphere as people exit the cinema, continuing the tone of the movie and I think helping it stay in the audiences head longer. And, conversely, few things are more annoying than a poorly chosen song immediately undercutting the film's intentions and jarring with the accumulated experience.

This thread was inspired by how wonderfully fitting Dinah Washington's "This Bitter Earth" was at the end of Shutter Island. So, does anyone have any brilliant/awful examples?