[update 24 January 2012] Apple has now released its own free app for creating interactive ibooks, ibooks author, intended for text books. Note that any books created with the program are only allowed to be sold through Apple and they take a cut of sales.
Note: There is a Kindle app for the iPad, and iPad users can buy Kindle books from Amazon. It might be more worthwhile just developing for Kindle as that’s more versatile (you can read the same book on a PC, phone… or iPad). I’m guessing this only works for static ebooks – if you have animation and interaction, you’d probably have to make the book for a single operating system (and format it for a particular device). But I’ll have to look into it more.
The following are still in development…
But there is Corona, which looks like it’s mainly for games – I’m guessing more versatile but more of a learning curve too.
The nice thing about Corona is they do not take a percentage of sales income for your apps, instead you pay them a license fee to make as many apps as you like in the year.
There are many other app development programs becoming available, and they all offer different terms – ie: some sell your app through their online store and place it on iTunes for you, but take a fee from each sale for this.
If you are already a techie app developer, you can download the SDK (Software Development Kit?) from Apple and be all set to get the app on iTunes.
If you use other software, do realise you may need to also pay developer fees to Apple to get the app on iTunes, and that is an annual fee, and Apple take a % of the sales (30% I think). The app is only on sale as long as you hold a developer license unless you go through another developer service and get it onto iTunes through them. – June Goulding, via illustratorsUK Yahoo group