E-reader formats

A poster on my Facebook page raised a good question about different formats for the book. I'm currently considering putting Chosen of Harrekh into the Kindle Select program. It reaches a larger audience, but you have to keep the book exclusively for Kindle for 90 days. So, I'd like to find out what e-readers other than Kindle my audience uses. (Nook, ibook, and any others I might not know about). If there's a lot of demand, I'll keep it out of Select. So, who's using what?

For right now, I'm not pursuing hardcopy publication. All of the print-on-demand options I've researched so far would result in a very high price - more than most people would be willing to pay even for an established fantasy author. I'm certainly open to suggestions, so please feel free to use that Comment link!