Easy with the melatonin. That is to reset your circadian rhythm, not get you to sleep in a jiffy. It sounds like the OP does not have a problem with that, just in need a good white noise app.
http://www.rainymood.com/ is good if you have wifi. Not sure on a good app. They have free versions in the app stores.
If you are looking for medicinal sleep aids I would suggest Zzz-Quil.
Our humidifier is a sunbeam. We use it every night. requires weekly (the instructions say daily) maintenance.