On OSX, it's quite easy to create your own computer-read ebooks... If they're a plain text file.
Code:
say -v voice -f ~/file.txt -o ~/file.aiff
That command will read from the file named "file.txt" in you Home directory to an AIFF file in your home directory called "file.aiff", with voice being the name of a system voice (find them in the Speech prefs pane). It defaults to the preferences set in the Speech preference pane for voice and speed, if you leave out the "-v voice".