I posted this on another thread, but in answer to someone's question about popular formats, smashwords did a survey:
Edward Patterson published this helpful guide on publishing ebooks (his experiences and recommendations and he has a lot to say) It happens to be a free download, making it even more useful:
Me, I'm still learning. I can say that the biggest problem is finding a place where enough readers go. Amazon works very well for that precise reason. Tons of readers go there. For any other format, it's a battle to find the readers because there are simply too many sites--it's impossible to go to all of them to get one or two or 10 readers.
It's also a changing scene with new devices coming out and new converts to e-books joining daily!
(multiple formats; Amazon or Smashwords--$1.00)
Catch an Honest Thief
(Kindle only format: $1.99; a cozy mystery)