After a very patient education by my friends on MobileRead, I have decided to make the books available in the mobi format. Contrary to my expectations, given its association with the Amazon Kindle, the mobi format has been freed, along with associated software. From Wikipedia:
Mobipocket SA is a French company incorporated in March 2000 that created the .mobi e-book file format and produces the Mobipocket Reader software for mobile phones, personal digital assistants (PDA) and desktop operating systems.
The Mobipocket software package is free and consists of various publishing and reading tools for PDAs, smartphones, mobile phones, the e-readers Kindle and iLiad, and applications on devices using Symbian, Windows, Palm OS, Java ME and Psion.
This is a great relief to me because I no longer have to rely on external sources to provide Kindle users with copies of my books. I don’t have a Kindle, but I understand that they are able to use files encoded in the mobi format, so they aren’t completely tied to the Amazon book store. Now my readers who only have a Kindle ereader can get their copy with the least fuss possible.
I think that covers all the major formats now, for both the ebooks and the audiobooks.