When I published Viking back in December 2012, I had to sign an exclusive distribution deal with Amazon to get its help promoting the book on kindle. It turned out to be worthwhile; due to Amazon’s marketing muscle, I’ve had over 8000 copies sold.
Now the exclusivity constraints have expired, and the book is for sale on Apple’s iBook store, Nook, Smashwords (which offers several versions including pdf), Sony’s e-reader, Kobo, and the Diesel e-book store.
And by the way, check out the book extras that I’ve added to the web site–author notes, alternate covers, discussion questions, quotes, and so forth. Just look for “Viking” on the sivanea.com site menu.