Build your own nightmare! The Nightmare Kit sample pack include nearly all the samples used to create both Nightmare Lab and Return to the Wasteland. You can use it to create your own tracks under the Creative Commons Sampling Plus license.
(Image swiped from Kook Science Resistance – who knows where they got it from)
Update: You can also download it from the Psychetect web site if you don’t want to/can’t register with Freesound.