I like these Matt Gemmell's iBooks Ideas:
Your portfolio. Designers, developers, musicians, video editors… the list goes on. An interactive portfolio, showing your best work in the most effective way, complete with contact information and links to your online presence (or web portfolio pieces). For iOS developers, particularly, this would be powerful marketing.
Band biographies. History, trivia, music, live performance videos, photos and interviews.
I've been thinking about this myself the last few days and I think iBooks Arthur is an awesome way to create interactive music albums. You can listen to the songs of your favourite band while reading lyrics or enjoying looking at cover art visuals. Throw in band interviews and footage from their live performances and you'll have a sexiest album out there. I'm pretty sure bands and artists are working on this sort of stuff already. It's no-brainer.