Most everyone has heard of iTunes. Most are aware that iTunes sells both music and apps for the iphone, itouch, and ipad.
The thing is, Apple is quickly becoming the world's second largest seller of information behind only Amazon. And with 375 million devices, this is a massive opportunity to get yourself in front of buyers in an area that currently has nearly zero competition.
You can get your information added to the global itunes library and made available for purchase.
Getting your information to the top of a search for it is really as simple as getting some links to it. I like to use SmashBooks.com to get this started and from there a basic link building campaign can dramatically help get your information listed at the top of a search on iTunes.
And here's the thing. The growth of the iPad means that a HUGE number of people search itunes for information FIRST.
If you have information that you sell, putting it on iTunes, as well as making it available for the Kindle (using kdp.amazon.com) is an extremely smart thing to do.