i use these two mainly:
Brainhack
https://itunes.apple.com/us/app/brai...295462503?mt=8
Sleep Pillow
https://itunes.apple.com/gb/app/slee...410351918?mt=8
I can also second the audiobook and podcast idea, though that has backfired a couple of times when the book got too interesting
its probably best to listen to something youve already read. I love listening to Stephen Fry, he reads the british harry potter books on audio.
Also, Paul McKenna's "I can make you sleep" really does knock me out.. i dont know if its actually the suggestions that are working or just the fact that he is soooo boring he puts you to sleep