I just got this whitenoise app: http://www.tmsoft.com/iphone-whitenoise.html
I guess people use it to sleep, I've been using it to study and it is sublime! I got the free version, which only comes with a handful of sounds, but you can make mixes and other customizations to them. The only odd thing is that by default, the iPod control option is turned off, and even when you turn it on, closing the app stops the sound. You can then double click the home button and play from the iTunes control when you swipe to it. I assume this is just a minor glitch they have at the moment.
Thanks for the suggestion! I often study/read/sleep best when there's some ambient noise in the background. I used to put on RainyMood.com for these things. So goddamn relaxing.