Not trying to nitpick, but Pink Floyd is a (are a?) 'They'. It's a band. Sorry for being pedantic but it's a relatively common mistake that bugs me, mostly because Pink Floyd's one of my favourite bands.
Anyways, for contributary purposes....
A lot of the ambient tracks from the Portal 2 soundtrack are pretty creepy. Good examples are Overgrowth, Ghost of Rattman, and Haunted Panels. Best of all, all three volumes are free!